Can Someone Tell Me, How I Dump Her?

I recently told this girl i want to go to 3rd base with her. today we made out a bunch and stuff. I always planned on having our little fun at 3rd base and quitting there. She texts me like 5 times a day wanting to be more serious and stuff like that. Also if anyone finds out about this my life is over, she's thought of as ugly and stuff I'm hooking up with her purely out of my desperation(ill admit it) and i want it to end. After 3rd, how do I end it with her and like make her not want to be all buddy-buddy with me? Please give me a helpful answer, instead of telling me how what im doing is wrong, cuz i dnt giv a ****.