Okay, what you do is have a movie date or something, and have her pick out the movie, and make sure it's something sort of romantic, to get you both in the mood for having sex, or her giving oral, etc. And hey, most guys' penises at your age aren't big, and you're still going through puberty, so it's probably not done growing. She should just accept you, and most girls don't care about penis size. Just make sure you are both ready, and make sure you don't make a big mistake with her by having sex. You two should be in love, not just doing it because it feels good. I would be extra safe at your age, and make sure you wear a good, trusted brand of condom, and make sure she's on the pill just in case anything happens. Sex is a serious thing, and it shouldn't be taken as a joke. Good luck, man. Make good choices.