Avalon,
Here is my advice.
In a perfect world, where babies are born to loving families, abortion isn't necessary. In a perfect world, where babies are born without horrible defects such as profound retardation, water in the place of a brain, hearts on the outside of their bodies, abortion isn't necessary. Unfortunately, we don't live in a perfect world.
If you have the child and decide to raise it, consider the following.
1. You don't have the income to support the child, and you will most likely live in poverty OR push the child off on your parents.
2. You will not be able to work, because you will be a full-time mother without a father. Again, poverty.
3. You will be devastated both emotionally and physically. You will be tired, overwhelmed, and very angry at the world.
4. Your chances of marriage will decrease about 99%. Men don't like to marry women with kids. Chances are you will be single, or you will have to compromise in a big way, by marrying a loser. He might even molest or abuse your kid.
I know this sounds harsh, but this is the real world. Have the abortion and ask the father to help with the cost. Get some counseling afterwards. Start using birth control and stay in school. Never look back in regret over a bad mistake you made.