Well, obviously if she's scared to have sex then you have to learn to wait and be careful about it. You just can't expect her to jump right into it. This must be her first time or something, because if she's scared your going to hurt her, thats a big sign.

Your going to have to learn to be patient or else you'll just end up making her upset and you'll get nothing in the end (plus a loss of a gf). Don't pressure her. Almost go all the way, but before you do, stop and ask her if she's alright. Talk to her about how to ease the pain, if thats whats causing the worrying. Buy some lube and try to get her to relax.

This shouldn't be ONLY about you! All you care about is getting some. Try figuring out what SHE needs first. Put her needs above yours.