We are 15, how can i make sure he doesn't try to go too far?

we are both 15, he is a player. we've made out twice before, and i know he has fingered girls/ gotten blow jobs. last time we made out in a public place and he like un did my pants and tried to finger me in public... but i didn't let him because we were in a place where people could see. so i might hang out with him again tomorrow but i don't wanna be fingered, i don't feel comfortable doing that yet. last time i was like "no, not here" but he was sorta pushy and like "just for a second" or whatever. i dont even get what guys get out of fingering girls anyways. im gonna stop rambling now, just how should i make sure he doesn't try again?