Lucky.
I recall a specific occasion, I still recall it vividly.
I was lucky I made it home. I think I nearly went emo. I'm not sure what happened after the rejection, things just got hazed.
I don't know if I'd advocate acting so carefree though, at least not in front of others. Perhaps I'm just really cynical of the opposite sex, but there does exist a chance that it was some kind of cruel test. Besides, sometimes pity is just what you need for another chance.
Now, on a more serious note:
From the context, it seems like you're still in high school. If so, that explains a lot of it. High schoolers are marked generally by the quality of not knowing what the fsck they want. Not to offend them, but maybe 95% of them just don't know. Being generous, 5% might seriously know what they want out of life. Chances are is that this girl was just as confused as you are. Thought you were cute, liked your personality, then the feeling faded for reasons unknown. I know that happened to me plenty in high school. I got a crush, then the next week was winter break or somesuch, and then when I saw her again, I felt nothing. It happens.
Don't be discouraged though. I would highly recommend being friends with her. Not only will it keep a chance alive, it will increase her respect for you when she sees how mature you're being about it. Show her that you don't mind the confusion and still want to be friends. Show her that you're a man that is wise enough not to sweat a misunderstanding.
So her crush faded, doesn't matter. You may get lucky. She may begin to love you for who you are rather than who she thought you are. Show her some stability. High school years generally tends to lack that... she might appriciate it.