Hey Borntoshop!
I'll be glad to help you =]
Nit-piks first;
All through class I got notes chucked at me - 'All through class, notes were chucked at me.' - Flows better as it's inportant that the opening line gets the readers attention. Even if they've read the first chapter, readers will still be put off if the opening sentence isn't attention grabbing or if it lacks flow.
one’s that made no sense at all like:
How could you say that about your best friend?
- Instead of putting this. You could say how she caught one of the letters and read it; e.g. 'I'd caught one of the notes that had been directed at my arm. Opening it up, I'd felt myself frown. It didn't even make sense. 'How could you say that about your best friend?'' - It's only a suggestion/ a guideline for what you could re-phrase it as.
Say what? - You should put her thought in italics so it's clear to the reader that it's what she's thinking.
I had just lost my Best friend I don’t even know how, and the whole school hated me. - I'd turn this sentence into two. 'I had just lost my best friend and I didn't even know why. Not to mention the whole school seemed to hate me for it.'
All through the rest of the day I would get yelled at when I walked down the corridor and tripped up. - I'd re-phrase this sentence. 'Throughout the rest of the day, I was getting yelled at and tripped up when I walked down the corridors.'
Not even the slightest idea I didn’t even talk to Monica last night, apart from one text - Add in a full stop after 'idea'
After that I went into my own little dream, thinking about everything I did last night. - 'I did' would sound better as 'I had done'
(so I couldn't’t have done anything there.) - I don't understand this part 
When I got home I had a lot of school work to do, I had a text from Monica asking if I wanted to go to town i text back saying I couldn't’t I had homework. - This sentence is just one big blur. There isn't any punctuation where there should be. 'When I got home, i had a lot of school work to do. Chacking my phone, I saw that I had a text from Monica, asking if I wanted to go into Town. - (Here add in how your MC feels about getting the text...surprised, happy, annoyed?) I text back saying that I couldn't as I had homework. (Was the homework an excuse not to see Monica or did she genuinely need to get her work done? You could add this info in so that the reader knows why she didn't want to go out)
(Was she made about that? I don’t think so) - I don't get this either. Is this whole paragraph a daydream about what she did last night? If so, you need to make sure that you use past tense so that the reader is aware of this.
'When I had gotten home' - Instead of 'when I got home'
“Hill!” Nick snapped me out of my thoughts. “Come on we have gym.” - 'Nick's voice snapped me out of my thoughts. "Hill! Come on, we have gym."'
Great! Just what I need. Now I really would be showing my legs. I thought as we walked across the court, toward gym, - Insted of saying that she thought it, put her thoughts in italics. Great! Just what I need. Now I really would be showing my legs.
When I walked in I realised I would have to walk into the girls changing room alone. - Explain how she feels about having to do this. Sick, nervous, like she wants to cry?
Yeah he could say that I’m going to die in there - Italics
of towards - 'of' should be 'off'
When I opened the door the girls stopped what they were doing and stared at me. - Comma after 'door'
“Oh, look here's miss-i-cant-do-anything-wrong.” Someone said across the other side of the changing rooms. - Describe the voice. Was it full of hate, sharp, nasty?
but I didn’t feel any better he couldn't’t make this go away. - 'but I didn't feel any better. He couldn't make any of this go away.'
my bag trying to ignore the cold - Comma after 'bag'
When I got to my bag tears weld up in my eyes, and I couldn't’t handle it anymore. - Comma after 'bag' and 'weld' should be 'welled' You also have an extra 't on 'couldn't'
When they knew I saw it they all cracked up laughing. - 'When they realised that I'd seen it, they all cracked up laughing.' - How does she feel...embarrassed, upset, distraught?
of the seat - 'off of the seat'
When I got outside all the boys were standing - in a big group chatting about god-knows-what with a strong smell of links in the air- waiting for all the girls. - I'd re-phrase a bit. 'When I got outside, I noticed all of the boys were standing in a big group, waiting for the girls. The sound of their voices rang in my ears and the smell of Lynx hung thickly in the air around them.'
He said worry in - Comma after 'said'
I pushed through him - 'I pushed past him' would sound better.
It had only been a day - Full stop after 'day'
I don’t even no why everyone hates me so much. - 'no' should be 'know'
I ran the whole way home I couldn't’t stop or slow down, it was like I was programmed at that speed and I couldn't’t change it. - 'I ran the whole way home, not even stopping once. It felt like I was programmed to run at a constant speed and I couldn't change it.'
Once I got home I started to run up the stairs and I heard shuffling in the kitchen. - 'Once I got home, I started to run up the stairs when I heard shuffling in the kitchen.'
Why are you home.” - Question mark after 'home'
“Early closure?” I said by mistake I made it sound like a question, but he didn’t notice. - I'd re-word this. '"Early closure," I lied and thankfully he seemed to believe me.'
When I got up stairs I fell to the ground and curled myself up into a little ball. - 'When I got to the top of the stairs, I fell to the ground and curled myself up into a little ball.'
Oh, hello Nick - Full stop after 'Nick'
I said as i tried to pick myself up a bit make myself look a bit better but I didn’t have the energy. - 'I said, attempting to sit up, but I didn't have the energy.' - Add in why she didnt have the engery...was she tired from crying? From thinking about school?
it sounded so stupid of course it was my bag.. - 'stating the obvious' instead, maybe?
his face went all sympathetic. - show don't tell - did he raise his eybrows ect...
someone the, dean?” - Full stop after 'someone' and take away the comma after 'the'
‘What did I do?’ - italics
me to or - 'to' should be 'too'
them full. - fall?
He shook his head and came and sat next to me again. - Did he even get up?
I pulled a smile onto my face but I didn’t feel any better, somehow I’m sure he would end up hating me too. - 'I forced a smile onto my face, but I didn't feel any better. Somehow I was sure he'd end up hating me too.'
Overall;
Don't be put off by the amount of nit-piks. Most are my opinion so you an choose whether you listen to them or not.
Make sure you take the time to let the story flow as sometimes it seems a bit rushed in places.
Put the thoughts of your MC into italics so that it's clear to the reader that they are thoughts.
Read it aloud to see if it makes sense. It also allows you to find out where commas need to be placed - by where you take breaths in a sentence.
Make sure you take the time to express how your MC is feeling as otherwise she may seem emotionless. As Rosey Unicorn told me; characters are 90% emotion. Without knowing how your MC is feeling - she seems less realistic.
I will say that your grammar has improved a lot since I first started reading your stories, so well done for that 
The story is still interesting as I'm curious to find out what your MC did!
I think you have potential as an author and if you take my comments into consideration then I feel that your stories will really improve. We all learn from our mistakes - me included
Hope I've helped and don't hesitate to ask for my help again in the future 
Good luck and keep writing!
xDudettex
but good. if this really happened to you then that really sucks. I sympasize with you! okay just a couple of things...(I'm the least picky. I mainly focus on the story)
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