Well, if it's any consolation...
My big challenge at this point is to come to terms with how I feel about the slug she got the other half of the DNA from.Wasn't I reading the other day that the male donation is actually only 1/3rd of the DNA?
I think your feelings are understandable, though a lot depends on how fast your child can grow up and handle the tremendous responsibilities. My sister had her first child when she was 17, though in that situation her husband-to-be was willing to support the child by going to work. That's been some 17 years ago and they are doing quite well - HS graduation comes up this year.
Then again, my sister-in-law from my wife's side just left her loser of a husband. They have four kids with one that's just 3 months old. She moved back in with her parents who are now helping to take care of the kids. She didn't have her first child till she was 24, so I suppose age isn't always the essentially ingredient in these matters.
Still, it's an awfully young age to come to grips with being responsible for infant. I wish you the best of luck. The only good news is that as a young grandparent, you will get to actively enjoy your grandchild.