This is a pretty common wish, I'd wager. Know everything you know now with no responsibility. Ace school cause it'd be like a review. Friends and romance would be much, much easier with your experience. You would be SO free simply be knowing it's such a waste of time and energy worrying about certain things (am I normal, does she like me, am I ugly, etc.)
Oh to just sit back and relax with nothing hanging over my head and no responsibilities (compared to an adult). Oh, to have that very strong feeling of wonder and know your while life ahead of you and the possibilities are endless!