Also, use lubricated condoms. If you are using non-lubricated ones, it will not help things at all. (What, you're not using condoms? OK, think, think, think. Do you want to be a daddy?)
First of all....LOL....you shouldn't be having sex at 16. That is just the mommy in me talking. But now for the advise.
well...there really is no way to correct this problem. If neither of you have had sexual intercourse before, it could be painful for her. The skin in the vaginal area is full of elastic forms, but your penis could be a bit large for her at this moment. Try a bit of four play and massage that area before going further. Take it slow.