A few options:
1. Abortion. But you'd have to sit her down and have a sincere talk about it.. A lot of girls are very unnerved by getting an abortion, and it's a hard topic to sit and seriously consider. She may not want an abortion for several reasons. But it's still something to discuss. I am pro-choice, and she may be too, as may you be, but when it comes down to makin' the decision for your own self, it's hard to do.
2. Keeping the baby. Another hard decision. Whether or not to stay together. Whether or not to try to raise the child together. Whether to get married, or how you'll live together. Or maybe how to handle being a family but not needing to get married. Marriage is not necessary, don't sweat that. If you don't know her well, it's best not to get married because you'll be with a stranger. But definitely spend more time with her and get to know her no matter what decision you BOTH make.
3. Adoption. You'd be surprised how many people adopt out. The only issue here is that a lot of women get real attached during the pregnancy and may suddenly change their minds about adopting their child out when the time comes to do so.. It's something to be discussed of course.
Have a sit down and talk with her about these options. The best one, in my opinion ( so take it with a grain of salt ) is abortion. It's hard growing up when you're parents are both young and unsure. Take it from me.. I've seen it, felt it, helped people through it.. I had to take care of my girl's baby for a few months while she was trying to find a place to live after her boy kicked her out. They had tried to force a relationship for the child's sake and it had not worked. That child is almost three now, and you can see the rage in his eyes. Children who grow up in that situation can either become mental, or grow through it and become great people. I've seen both. I've seen relationships spring from these situations, and I've seen them crumble as well..
It's all about talking it over.. and seeing what the both of you decide. It's a hard situation to manage, but take it a day at a time. If abortion is too hard for her to deal with, you have to decide whether or not to stand up and try to work out a relationship with her. If it doesn't work out, then you are the father and you do what a father does.
Talk to her though, ASAP, and ask what she thinks.. If she's all confused and scared as well, it's normal.. but she has to be an adult in this situation. It's her child too, obviously, and if she can't grow up and be the mother then there's no reason to keep the baby.