Is something wrong with me?

So, I have a pretty fat ass. Not bragging, it's just a fact that I have a fat ass for a while girl. I'm pretty confident in my body, but that doesn't mean that I only wear tight clothes. Anyways- it seems that every single guy that I'm into, all they want is a quick fling. All they want is sex.

Backstory: A month ago, my ex spread a rumor around my school that I had sex with him. Everyone started to hit me up and ask for nudes & shit. I tried to tell them I wasn't like that & I wouldn't have done that at FOURTEEN, but no one believes me.

What can I do to give off the impression I'm not a slut?

Sidenote- I'm sixteen.