So basically you declared your interest, and she turned you down. Are you still spending time together, or have you stopped meeting each other?

What you should do about it depends on her reactions. If she was ambivalent, kind of maybe, maybe not, then I think you should push for it, it's very hard to resist someone who really shows interest for you.

But if her rejection was frank and without appeal, then you just have to accept it and let that story rest. You won't be the first to whom this happens, and however painful it is, you need to learn to move on, in order to one day find someone with whom you can have a fruitful relationship.