Just don't "do it" with her until you're over 18. The only ways not to get her pregnant are not to do it, use a condom, and use birth control. But, the only way you can guarantee that she won't get pregnant is that you just don't do it.
Well if you use the term "do it" you're to young to have sex anyway.. But condoms are 100% if shes on birth controll you shouldn't get pregnant but she still can. You could always use the high school shit and pull out before you cum.. Or just not have sex..
Dude, wear a condom. Don't be stupid. 30 seconds of unprotected sex is not worth the risk of 18 years of parental responsibility. Clearly you are not ready to be a father. Exercise some self control and responsibility.
Well she can use a female condom, or take birth control. But, like others said, wait. I don't know how old your are, but if you DO get her pregnant, then you will have a lot of hard decisions and a tough early life ahead. Be smart.
If you do not know, you are not old enough to sleep with someone. Ask your parents or Dr. If you don't dare to: see the beginning of my answer. In short: yes, there are plenty ways: pills, injections, inserted contraseptives. My advice: just wait a little while. If you don't want to: again, please speak to an adult you can trust.
If you don't want a baby. Do NOT. Have sex. That's the only sure way. You also shouldn't be having sex with anyone until you're sure that persons the one you want to commit to. You have to be quite mature to make that decision.