Do you think abortion is wrong? Maybe you think it is morally wrong, or unnatural, or that women should have babies, or that interfering with god's plan will send yuo to hell. Maybe you just love babies and don't much like women who don't.
There are plenty of reasons to be opposed to abortion. You might even choose to not associate with anyone who would have one, has had one, or doesn't think they are wrong. You would never have one, under any circumstances. Perhaps you write elegant arguments in journals or blogs or spray paint them on your roof outlining your beliefs, hoping that you will convince other women to think like you do.
Great -- all that would make you "anit-abortion".
Where it steps over the line, is when you want to make it ILLEGAL and PUNISHABLE for anyone else to have an abortion. Then you are anti-choice. My objection to the term "pro-life" is that it is the name used by a semi-organised group who want to make abortion ILLEGAL and PUNISHABLE. What they are is opposed to allowing women to make that choice for themselves.
Being anti-abortion is one thing, but you can be that without trying to punish other women who don't agree with you. Try to convince them if you feel the need. Be anti-abortion. But if the only way to persuade someone that you are right is by taking the choice away from them, then maybe your arguments don't stand up.