This needs to be moved.

If your girlfriend is late she needs to take a home pregnancy test. It should be accurate at this point. There's no way to stop her from getting pregnant because she might already be. If she is, you should go to a planned parenthood and see a counselor to look at all your option and deal with it from there. You need to support your girlfriend in her decision though because she is the one that will have to deal with a majority of the consequences.