I understand what you're saying, but this is your child, you helped make it! It's really stupid for you to not want it because "it doesn't fit into your life" right now. That's not a man honey, sorry to tell you.
1. You made the choice to sleep with the girl
2. You made the choice not to use any birth control
therefor you made a child. :d
think about this baby in 10 years, asking about it's dad, I didn't have a dad my whole life either, and when I was little I did cry over it because all my friends had fathers and I didn't. It might not effect everyone not to have a dad, but this is your first kid and you just want to walk out on it?
It might not seem great right now, but you need to tell your girlfriend what happened, and I think you need to start being in this girls life, you're always going to have a connection with her now, through your child. Step it up, life doesn't always go the way you planned..