Went through a similar situation in high school. I had been hanging out with this guy, never did anything with him other than kiss and flirt. I'm not sure if my friend was jelous or what, but the whole next year I was dealing with rumors that I "let him hit it.". I was sooo upset. I thought he was spreading them, so I confronted him. He swore up and down it wasn't him. Then a friend of mine told me that one of my closest friends was telling people that, so I casually asked her if she had heard the rumor. The look on her face gave it away even when she tried to deny it. She told me she knew who started saying stuff, but she couldn't tell me because it was a good friend of hers. Me and her had been friends for YEARS and she couldn't tell me? Yea right.
After a lot of other stuff, I ended up just dropping her as a friend. Ignored her completly, and when people asked me why we didn't talk, I told them she just wasn't a good friend to me and left it at that.
You don't need to get back, but in a way just dropping her is a way to get back. Who cares about her anyway? Truth is you probly won't talk to her or half the people you do now once high school is over. And people do forget, so just stop aknowlegeing the rumor and it possibly will go away.