Hi Justin, 

Thank you for sharing your question. I'm sure a lot of your friends have similar burning questions, but are too shy to ask.

There are a few issues here:

1) A girl could already be pregnant before you have an encounter with her. How would anyone know?

2) After you masturbated and ejaculated and urinated, there is still a good chance that there can be some semen left behind, which in the right time and space, can possibly lead to a pregnancy. Albeit, the chances are slim.

3) 3) Even if you haven't masturbated earlier, the fact that it was probably unprotected intercourse means that there is still a good chance of pregnancy, even if you did not ejaculate inside her. You could refer to this scientific paper for more reference.

4) Did you mention that you are 16 years old? Possibly your girlfriend is 16 years old as well? In any case, it could jeopardise your future. You could read up the law here if you are interested. 

5) "The rest of my friends are doing it." But certainly, both of you could visit a nice GP, who can talk through all these issues with you without judging you. Perhaps using protection would be a good idea.

6) 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.