You have been sending this girl mixed messages so its no wonder she is ignoring you right now. The best thing to do is next time you see her, say "Hi!" if she talks back to you then all is good, if she ignores you again that its not so good. My guess is that she will speak to you as it sounds like she was definatley interested in you at the beginning, now you just need to let her know that you are still interested in her. If you can get a conversation going, then just come straight to the point and ask her if she wants to do something after school sometime. The worst that can happen is that she says no, then at least you will know where you stand and you can move on from there. Good luck!!