ok dude listen up. Im 13 too and live in brooklyn. Im always being pressured about what to wear. I cant wear jeans too tight or they'll laugh at me. This is what i wear, and people dont say shit cuz they cant. OK i usually wear baggy pants not too baggy like thugs and shit. I wear polo, tommy hilfiger, and nautica t-shirts, nothing like ecko or anything other of that shit. I am kinda chubby too, im 5'9" and weigh 166 lbs. I got muscles though so im not all that fat. All i could tell u is to lift weights and do sit ups
and all that other shit and ull be fine. Im in a same situatuon right now, i really like this girl. Im to chicken to go up to her and have a conversation cuz shes always around friends. I got her sn though. I just work it step by step idunno what to tell u. Good luck........
PS, ask some friends that r girls at school what to do.