Relationships, What should I do now? Options

[xichimonjix]

This could turn out to be a long story, but...ok, so there's this girl that I like at my school (We're in Gr. 10). We're friends, and we see each other a fair amount outside of school. I wasn't sure if she already liked someone else, but a few of my friends had said that she did. I hadn't noticed anyone that showed that they liked her though, so I decided to tell her that I liked her. Only recently, I managed to say that I did like her, wanted to be with her, and asked for a chance to be her bf. She said that we should remain friends because she thinks that our relationship isn't strong enough. I'm not quite sure what to do now... Even after being rejected, I still feel that I like her though. It didn't change the way that I felt. Should I just give up or could I try to develop our relationship so I could ask again later (I think that she likes someone else though...) ? How can I develop a better relationship (I'm kinda shy)?

I would be grateful if I got some good advice, thanks.