Hi!
The first thing to do is to get a pregnancy test. If you have access to a Planned Parenthood Clinic in your area, they can do a test for you and can discuss all of the options for unintended pregnancy and also birth control.
Hope this helps!
Dr B
If she is in fact pregnant, there is nothing that can prevent the pregnancy now. If you both agree that you would like to end the pregnancy, then you can look into abortion. Here is some information on abortion:
http://familydoctor.org/online/famdocen/home/articles/846.html