You may want to look into Plan B emergency contraception. It's most effective when taken within 72 hours of intercourse.
Sorry to say, but you had intercourse at the worst time if your looking to NOT get pregnant. About 14 days from the first day of her period is the most fertile time to get pregnant. Hopefully, the condom had spermicide, and could kill off some of the pre swimmers....yes, they do exist. Some will rebuttle that, but you can't be too safe. You'll have to wait until her next period is due, and take a home pregnancy test. Good luck...