Hi. Is it possible you came before you pulled out? Could be. Also, if you had ejaculated within the last few hours prior to seeing your girlfriend and had not peed several times, there is the chance that your pre-ejaculatory fluid could have carried some live sperm in it from inside your urethra into her body. That's why the "pulling-out (so called) 'method' of birth control" is not really a method of birth control. 'Pre-c u m" can sometimes have sperm in it.
Is there any way to stop a pregnancy without abortion? If this happened like, last night, she could take what is called a morning-after pill (marketed under different names in different countries, called things like "Plan B," and available over-the-counter at the pharmacist's.) But Plan B won't work if this was several days ago. I think it's supposed to be effective (with a 7 out of 8 chance) if taken within 48 hours of the unprotected sex. I don't know for sure but think it's max time range it can be taken and still possibly be effective is 72 hours after the sex. But don't have her take it if the time has passed, it is not a good thing for a woman's body to take Plan B randomly. It's meant as "emergency contraception," not meant to take the place of her getting on the Pill or having an IUD put in.
Do you need to try to stop "the pregnancy"? Not if there isn't a pregnancy. It takes sperm and an egg to produce a pregnancy. You know you produced sperm but did she produce an egg? That would depend on her cycle. A woman only produces an egg once a month. If she is about two weeks before she is expecting her next period, that would be the most likely time to get pregnant. If she is one day before her next period is due, it is unlikely she got pregnant because she would not have had a viable egg in her system at that time. So, talk to her about her cycle and where she is in it. Most women keep some kind of a record.
If she decides to keep the baby what do you do? This presumes, first, that there is a baby, second, that the pregnancy will not end in miscarriage, third, that she will choose to have the baby, and fourth, that she will not want to put the baby up for adoption. But if so, well, she does have the right. If you two are teenagers, that will be difficult, but you don't get to tell her she can't. And since you were\ are as responsible as she for the actions that produced the baby, you don't get to walk away. I'm sorry if that sounds unfair, but nobody put a gun to your head and forced you to have unprotected sex. So, in answer to your question, if there is a baby and she keeps it, you will be required to pay child support. Hate to say it to someone who is freaked out, but if you made a baby, you owe that child to see that he or she is well cared for until he or she is legally an adult.
I'm hoping that she didn't happen to be ovulating when the two of you had your event watching a movie. If she wasn't, all the rest of this concern is going to be moot. I'm also hoping you get a whole lot more educated about birth control and take it seriously. Condoms were invented for a reason. Please take this event as a serious lesson in what could happen.