Welcome to the board.
One piece of advice that's hard - don't second guess yourself or your decision. You made the best decision you thought that you could at the time. You obviously didn't make the choice lightly. Accept that you did the best you could, and forgive yourself for being in the situation where you HAD to make a choice. You didn't try to be in that spot. None of us do.
As for how to come to terms with it and cope, I'd suggest finding someone that you can talk to who is supportive. Don't be afraid to talk things through with them. You'd be surprised how much support you can find in friends you wouldn't have guessed would be supportive.
Also, if it continues to be a problem, don't be afraid to go into counseling to find some help dealing with the decision. A professional who you can trust may be able to help you cope.
Finally, don't forget that you did lose a baby - even if it was a voluntary termination. It's still a loss. Allow yourself the space to grieve for what you've lost. Some people have a naming ceremony for the baby. Some have a sort of service for it. Some burn the ultrasound photo, to send it to a higher place. Whatever works for you to mourn the baby isn't a bad idea.
I hope that helps, but above all, try to forgive yourself for making the best decision that you could at the time. Should have, would have, and could have's don't count now. It's easy to second guess - but making the choice was a brave thing - no matter what you decided.