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Okay, this is persuasive which is a pluspoint, I guess. What I would say is you need to watch some sentences such as this:

If I can get into a good college because of the IB academy, I would be ensured that this would be true. Attending CIBA would ensure that my future is open to all the possibilities I want.

See the repetition of the word, "ensure"? It needs to be replaced, or it'll sound like you're trying to hard. Also another part of this quote doesn't sound right, re-read this:

If I can get into a good college because of the IB academy, I would be ensured that this would be true.

What? Structure it some otherway. In persuasion you need to be 100% clear to strengthen a good argument.
Personally I think you've done really well. It's just the right length and doesn't drag on. The language chosen is generally good. Remember to vary it in persuasion though to hold the attention of the reader and make it seem effortless.

My creativity would be a worthwhile contribution to the learning environment, and would benefit CIBA’s already talented pool of students.

Okay, I do admit this is a good ending. I think you should put something else instead of "Your creativity" because you've mentioned that you have this to offer already. Stick in another quality about yourself. Don't be modest. This is your time to boast, so boast!
All-in-all its good, just give it a bit'a thorough revision first!
Hope this helped,
Ben.