If you decide to have the baby:
I know some couples with children living happily as a family. How
they got the children was just like your case, an accident.
I know some people who end up in trouble, got married just for the
sake of the child. Then they got divorced and the girl become
burderned by the child and become a young toutured single
mother.
however, abortion:
Everything will end and the only thing bad was the mentel and some
physical problem hunting for the rest of your life.
Don't listen to all the advice above on you are a killer or
whatever. The choise is yours and your GF's to make. I know you
will feel guilty and sad but you have no choice. But if really
must, Get out from this forum and go to a counceler. They keep
everything confidential and have plenty of advice. They also have
many numbers of docters you can call to find out, the options you
have and they will always respect your decision. You won't get much
advice here except flames.
Good luck to you and your GF.
By the way, how old are you?