It happened with one of my friend as well but she was not pregnant. actually he told me that it happens with girls sometimes. Not coming of period is a different case. It may not be just because of your fingering or precum. There may be other issues with the girl as well. So better go to nearest doctor and follow their advice.
Hi if it is two months ago please put your mind at rest with a Pregnancy test , i very much doubt if your gf is pregnant from what you have said , there may be some anxiety with the both of you but please do the test , take care ,