I'm sure a lot of your friends have similar burning questions but are too shy to ask.
After you have masturbated, ejaculated and urinated, there is still a good chance that there can be some semen left behind and consequentially, sperm. The presence of sperm, no matter the amount, carries a possibility of impregnating a fertile woman no matter how slim the chances are.
Therefore, even if you haven't masturbated earlier, unprotected intercourse will always carry a possibility of a pregnancy, whether you ejaculate inside her or not. You could refer to this scientific paper for more reference. The production of sperm and the production of precum are by two different organs; the former by the testes and the latter by the Cowper’s glands. Theoretically speaking, precum does not contain sperm. However, since both pass through the urethra, precum can pick up residual sperm on the way out.
In any case, having underage sex may expose you to legal repercussions; it could jeopardise your future. You could read up the law here if you are interested.
I recommend that both of you visit a nice GP, who can talk through all these issues with you without judging you. But, perhaps using protection would be a good idea.
Other than that, what follows is my personal opinion: If you are ready to marry the girl and deal with any consequences, that is great. It takes great courage to do so. Even then, taking care of children when you are 16 years old can be a great struggle, and we have seen many children suffer in such environments.
