As others have said, it is quite easy to get pregnant very soon after an abortion.
However, if you don't want another child and don't want pregnancy to interfere with your schooling, then abortion is probably the best decision you can make, regardless of the fact you just had the procedure done. If you know you wouldn't be able to provide for a new baby, it would probably be more humane to abort it than bring it into a world where it may not have everything it needs or to stick it in a foster home where it will have no real family until it's adopted (which is a maybe).
If you don't want another child, you will be doing yourself and the child a great service by not bringing it into an environment where it's not 100% wanted. Also, you're in your last year of college - you're so close to your career that you can almost taste it. It would be a wasted effort to have to drop out in your final year for the child or to get your degree and be saddled with a sprog post-graduation.
If you are, indeed, pregnant again, please do not let anyone make you feel guilty if you wish to have another abortion.