The best thing you can do for your gf is just to be there and support her through this time. She is going to be going through a lot of changes physically and emotionally. Be strong for her.
I advise you to talk to your parents about this situation as well. Maybe as grandparents they can take their grandparents rights to the child and help you raise the child (if that is what you want).
This is a huge responsibility and you are included in this as you helped father a child, be the man and adult and offer your support, insights, advice and friendship. She is going to need these things more than anything. If they/she decides to keep the baby be there as much as you are allowed, go out shopping for diapers, food and clothes when needed.
Go with her to appointments, to prenatal classes with her and if you 2 decide to keep baby - go to parenting classes. These are suggestions that will help you as a couple and as the family you are having.
Hope this helps and good luck
*Remember use protection and you will avoid the pregnancies*