Just prepare for the big day when you're actually ready. Read a sex ed book and educate yourself on safe sex, so when it does finally happen, you know what you're doing. Although seniors are kings for now, they generally take easy classes and go home early. At some schools, seniors go off campus for lunch. Some don't come back after lunch.
Some don t go to school at all, or so it seems.
With that said, juniors have a lot of time to be the big people the campus. You should have your driver's license. You may even have your own car if you're lucky. If not, borrowing your parents' car isn't that bad, but you should start looking into getting your own car. Talk to your parents and see if they'll help you out.