First, you are on the right track by looking for wisdom before making a hasty decision. It is good that you are taking responsibility, since you helped to bring your girlfriend and new baby to this point.
It is not always a good idea to rush into marriage just because of a pregnancy. Seek wisdom from your parents, pastors, or other trusted family and friends.
This is an admirable decision: It shows you accept responsibility for the situation and are willing to love and support your child.
There are many complications that result from abortion. Remember, you are a father from this day forward; abortion will simply make you the father of a dead child. Abortion also puts your girlfriend at risk. You might also suffer from severe depression. Abortion is a costly decision--not only financially, but emotionally, physically, and spiritually for both you and your girlfriend.
Remember, though, you are still responsible for child support. Why pay and not enjoy the benefits of watching the miracle of a child--your child--grow up?
Do the right thing, and know that we are here to help you.