Don't let anyone influence your decision about your abortion, you have to do what's right for you, and nobody else. By all means, listen to what people have to say, but if you don't think it's the right time to have a child, then that's your decision, and you are completely entitled to go through with an abortion if that's what you really want.
I can understand why you're scared, anyone in your position would be. I'm sure that anyone who was going ahead with an abortion would feel a sense of fear, of course they would, but I wouldn't go as far to say that because you are scared of something, it means you are uncertain. It's only natural to feel scared by it, but you'll get through it, it might be difficult, but you'll get there.
Having a baby while studying doesn't have to be a bad thing, though it's usually seen that way. I have a few friends who fell pregnant when they were studying, and despite wanting to carry on with their education, they put it on hold for a year and went back to it. Just because you are having a baby doesn't mean that you have to give up on your career and education, far from it, you can go back to that at any time.
Whatever you do, make sure it's the right decision for you. Everyone is entitled to their own opinions, but at the end of the day what's right for someone else, might not be right for you. Make sure that you are certain that having an abortion is right for you, please.
As far as university goes, I think that by letting them know about your unexpected pregnancy and the stress at home, would be reason enough to fail an exam. They have to understand that you're going through a lot right now, and may be finding it quite difficult to cope, therefore your grades will suffer. It wont harm them to let them know what has been happening, and they certainly wont treat you differently because of it. You aren't the only person in the world to have an unexpected pregnancy, you aren't the only person in the world to have stress at home, and you certainly aren't the only person to have an abortion.
Don't feel stupid about what's happened, this sort of thing happens a lot. You aren't the first person that it has happened to, and you wont be the last, many people find themselves in the same position as you.