I Like a Girl Who Doesn't Like Me Back, How Do I Get Her Out of My Head?

I've liked this girl for 2 years now, and I told her (we just graduated out of 8th grade) that I like her at a party, and she doesn't like me back. And for nearly a week now I haven't been able to forget her, I've just been moping around, self-loathing and hopeless. I really need some help to get her out of my head, thanks.