You are fucking cocky. You can sing relatively well, you are of above average intelligence and you wear lots of (too many) colours and for some reason you think you're the dogs bollocks. I beg of you, please don't lose that. You confidence is what is going to define you and is going to get through some shit times ahead. I hate to break this to you but this is the thinnest you will ever be and although you hate that now, there is someone who will make you realise how brilliant your body is. You are right to not care what people think, stop questioning that.
Nick is a good one, even when he's a dick. Forgive him for making you late to school every day and keep buying him cookies because he does come through in the end. Start talking to Jon more because he will be important and stop wasting your time with Mark, he's loves someone else and will do until we're 18. Something really horrible is going to happen soon and I won't say anything else because this event will make you who you are. You will stop wearing light blue and start wear black and wearing white eye liner which will be a gigantic mistake but one that needs to happen.
You need to keep doing really well at school, you're right to think its more important because it is. You have your friends now and being good at Maths IS COOL. Try and get better at Science but you'll never need it again after this so don't stage everything on this.
Pete breaking up with you is not the end of the world. It seems like it I know, its awful and you have been with him since you were 15 and I understand that its scary but in February you will meet Alex and you can move on from there. Speaking of Alex, don't send him that poem, that poem is fucking awful. Work harder towards your A Level exams and stop living your life in the drama studio its turning you into a weirdo. More of a weirdo. Stop having McDonalds Mondays, its putting you on a slippery slope.
This would also be a good point to start learning to flirt, it will come in handy.