I'm not sure if I like my girlfriend anymore?

Well basically ever since I've known her. she's always been kind of cold to me or distant. Or rather, this is the feeling I get from her. For example, we were both at this group thing at six flags and she stayed with her group of friends, all girls, and when I tried to be with her she basically told me to go away on two separate occasions. I can kind of get that she was kidding but that kind of sarcasm to me isn't very funny. I called her on the phone to talk about it and she said she still wanted to spend more time with me. The next day I asked her to do something and she told me she had to study for a test for summer school which she is in now. I guess she's studying the whole day. To me it just seems like an excuse to avoid me. Overall I'm just sick and tired of her coldness and aloofness and I think I've just become disenchanted with the whole relationship. I mean, I guess she's just shy, but it's almost gotten to the point where I feel like she doesn't even like me anymore. I've scheduled to something with her this week, so should I just try to fix all of this, or should I just break it off with her? I don't know what to do. I'm 15 and she's 16 btw. Thanks, and all answers are appreciated.