You're 16. So, naturally, you're self-conscious. Frankly, it might not be such a bad idea to wait a bit. You'd build up your confidence, you'd perhaps grow and your body would change a bit more to the way you'd like it to be, and let's face it, you're pretty dang young.
Without knowing this particular girl, we cannot comment on her desires or preferences. But for gosh sakes, don't just go jumping into a sexual relationship, with her or anyone. Go out on dates! Get pizza! Take in a movie! Go skateboarding! Walk around your town!
Just, get to know this girl before you try to jump her bones. You'll find out if she really is interested or not, or if she is so shallow and superficial that a slight weight problem bugs her.
True story - long before meeting my husband, I had a very, very hot relationship. Ya wanna know what the guy weighed? About 300. Wanna know what I weighed then? About 160. It is more than possible, but what happened between us was, we actually knew each other. Try that first, okay?