NE; 'I'll be seeing you' First roots. Help please :)

Knock Knock!
"Cassie... You can't stay in there all day"
I could hear my sisters muffled voice through the Vibrating music and the wooden door.
You there Paramorekid ??
The little chat icon in the corner of my computer screen, repeatadly popped up as i ignored
my sister through the sound of Green Day.
My fingers betrayed and started to type.
Yes Lewis.. and you know my name is Cass. I think that your dad is really mean for
making you baby sit and not pay you. Remember, your 17 and your out in a couple
of weeks.
It annoyed me how Lewis a.k.a Falloutboy101 relied on my opinion for everything that
happened in his life, wether it was about his dads' relationships or how he doesnt get
bullied, even though he go's to a school full of chavs and he wears Black hoods and
skinny jeans. Talking about him like that makes me feel bad because, even though i vowed
not to become addicted to the internet. Never to meet up with somone online, i had
actually become attatched. I've been told time and time again, that i should make friends
and spend 'Quality Time' with my family, even though i hate my sister and we share nothing
in common. I've been told to do alot of things but advice doesnt mean the same as doing it.
I raised up the volume after a few muffled calls from Kara and then she finally stomped off and
slammed her door across the hall, wich sent shudders through my room and i knew i was in
trouble from mom.
Im sorry about your brother, but i've gotta go now. My sister wants an arguement.
bye xx.
I knew as soon as i typed the last two x's, i'd definatly regret it.
Bye
Just before i Switched off the mac at the wall, I noticed that my online time was flashing at two hours wich meant that i was either gruonded or i owed my mother £20 pounds. With my saving for a new camera and low funds, i would take a grounding in open arms, but my mom wasnt that kind and i didn't really deserve some kindness after the countless garden Gnomes, destroyed in my tantrums. I was in big trouble.
When i reached the kitchen, mum was staring at me whilst in mid conversation to suzan. Umming and arring whilst staring at me, probably thinking of ways to make everything my fault.
"ok Hun. Tell dan that he has to listen ... Umhum ... Really? ... Umhum ... Well ive gotta go now."
She could tell i was getting impatient.
"Bye hunn"-Slamming the phone-"What was that about ?"
"Uh .. what ?" I had nothing to say.
"Why do you always blame Kara for YOUR mistakes !?"
My mistakes ? Was i the one who got caught kissing her boyfriend in moms car!? nope
"Fine, don't answer me but you need to get a grip and get over this obsession with goth and emo stuff becuase it doesn't make you cool. You don't do this. Your my little Cassandra and you used to wear pink little dresses and bows and the glittery mirror makeup"
"How does wearing a black hoodie make me a goth ? And i am not trying to act differently.."
"YES YOU ARE. You acting like tom before he joined the army. He had some identity crisis, started acting differently and then we lost him!." I couldnt believe she had mentioned Tom and compared him to me.
"Have you ever thought that i missed tom? Did it ever occur to you that i didn't want to move here and that ever since, i've been alone! Mom! I have no friends. The only people i speak to are my friends online and you wan't to turn them off! Its like ever since dad left, you have wished that i was gone!"
"Ever since Kara got a place in a good school, you have been a little brat and tried to ruin everything for her! Stop being selfish and MAKE FRIENDS"
"It was YOUR fault that dad left" i stormed out and slammed the door for extra effect.

Do you think i should continue writing?? and please critique i was really hoping to finish this and keep it.

here is the plot: A lonely girl who is greiving over the loss of her brother, finds refuge in a boy who seems to understand her. As their frienship grows and she gets her life back, She discovers that she may soon loose her only friend forever.

Okay, so the general story was good, but there are a lot of grammar/composition errors here which detracted from full enjoyment of the story. I'll try to mention as many as possible here, so try not to be offended. I just know that it's hard to concentrate on a story when there are stupid little mistakes going on, which you don't want to happen to your other readers.

First off, I noticed a lot of improper apostrophe usage. For example,

...wether it was about his dads' relationships or how he doesnt get
bullied, even though he go's to a school full of chavs and he wears Black hoods and
skinny jeans.

The apostrophe in 'dads' should be between the 'd' and the 's', as now you are implying that there are multuple dads being referred to. 'Doesn't' should have an apostrophe in it, and 'goes' does not, but it does have an e. 'Whether' is spelled wrong and 'black' should not be capitalized. You should only capitalize proper nouns. Anything else that is capitalizes is taken to be incredibly important, and the color of his hoodie is not, regardless of whether or not it made the point of the sentence. Also, 'hoods' should, I'm assuming, be 'hoodie.'
An additional note which you might want to take into consideration--the usage of the word 'chav.' A lot of people probably don't know what you're referring to (I'm not even quite sure myself, I just know that it's some sort of 'stereotype'). If you are merely writing this for yourself, you can leave it like this, but if you intend it for a wider audience, you may just want to describe what you mean. Also, I'm not sure whether this name has a bad connotation to it, such as the connotation that goes with the word 'emo.' If referring to people like this, try to avoid using questionable terms in the narrative, for you will be restricting your audience. If you want a character to have issues with being called this name, that is one thing, but you as the narrator shouldn't be calling them this yourself.

Talking about him like that makes me feel bad because, even though i vowed
not to become addicted to the internet. Never to meet up with somone online, i had
actually become attatched.

The sentence structure here is really weird. This should all be one sentence. Try replacing the period with an 'and' and capitalizing the 'I.'

advice doesnt mean the same as doing it.

This phrase doesn't make any sense either. First off, more apostrophe issues in the word 'doesn't.' Secondly, you are comparing a noun to a verb, which makes no sense grammatically or to the reader. Always make both options in a comparison the same part of speech. Here, you could say, "hearing advice doesn't mean the same as following it."

bye xx.
I knew as soon as i typed the last two x's, i'd definatly regret it.

This needs more explanation as well. Why would the MC regret it? What does it imply? What exactly is the nature of the relationship between MC and this internet friend, being that he is the only one mentioned specifically? Try to detail this relationship more in the conversation and the thoughts had during the conversation, as this will add dimension to the story.

Just before i Switched off the mac at the wall, I noticed that my online time was flashing at two hours wich meant that i was either gruonded or i owed my mother £20 pounds.

This confused me. I understand why the MC would be grounded, but why would she owe her mother money? You should probably explain this more. Also, capitalize 'I,' but not 'switched.' You like random capitalization, don't you?

didn't really deserve some kindness after the countless garden Gnomes, destroyed in my tantrums.

First of all, more random capitalization. Secondly, what is this about garden gnomes? Random, much? The situation to which your MC is referring is definitely too obscure to be mentioned in passing. A larger explanation is definitely necessary.

When i reached the kitchen, mum was staring at me whilst in mid conversation to suzan. Umming and arring whilst staring at me, probably thinking of ways to make everything my fault.

Previous notes on capitalization aside, you have two major issues with this one. Firstly...Suzan. You mention her, but this is all. Being that the reader is not a member of your MC's family and thusly does not know anyone that they do, this is meaningless and confusing. Either provide more information or drop names altogether. Secondly, the second 'sentence' wasn't really a sentence at all, but rather a sentence fragment. A sentence at its simplest needs a noun and a verb, and nouns cannot be carried over from previous sentences without using pronouns. Therefore, you need to identify who is doing these things (aka her mom). The use of the phrase "umming and arring" isn't exactly the best, either, and you might consider paraphrasing this.

Another note, you don't necessarily need to transcribe everything that happens during the phone call unless it directly relates to the story. If you feel like adding something from the conversation, go ahead, but irrelevant "umm"s clutter the story and seem unprofessional.

Also, I would like to comment that the ending was kind of confusing because you didn't explain anything beforehand. Because this is not a finished work and you are planning on adding more to it later, this is more of a loose comment which you may listen to or disregard at your own leisure. I know that sometimes authors choose not to explain the situations of their characters at the beginning of their work, and this is a good thing because it avoids the countless paragraphs of dry information that writers tend to want to offer. However, you have offered so little information that at this point in the story I come off feeling as though I should know more. If you plan on continuing with a more detailed explanation later in the work, then this is fine and you can leave it the way it is. However, if this is all that you plan on giving on these aspects, I suggest that you make it clearer.

Now, I know that there were a lot of critiques here, and I just want to say don't be discouraged. Good grammar is an important thing for a writer, and many people won't take you seriously if you don't have it. However, with critiques such as mine, you can be more aware of what to look for in the future, thusly improving the way that you express your stories, which seem, from this excerpt, to be worth expressing. So, good luck and keep writing =)