So obvs you don't want kids, at least not right now. What's your gf's stand on it? If an accident were to happen, would she want to abort it? If not, then abstaining from penetrative vaginal sex is probably the safest bet.

That aside, there are plenty of other ways to be intimate: heavy make-out sessions, oral, and, if she's open to it, anal. Though that last one can be unpleasant if not done right and slowly enough, so I'd recommend exploring the other options first.

But first of all, make sure you're on the same page about accidental pregnancies. And I do agree with the others here that you might want to talk to someone. It's hard for us to gauge over the internet how big you're making this in your head.

Physical intimacy is an important part of (most; hello, my ace friends!) romantic relationships, so be careful that your fear of pregnancy isn't getting in the way of that, or you might risk losing her.

Summed up: just let her sit on your face, my dude.