A pregnancy is not impossible.
Plan B should
work. But don't assume it is 100% effective, as nothing is.
Take a break from all the humping and wait it out until she should be getting her next period. If she does not get her period when expected, buy a pregnancy test and follow its instructions to the letter
Consider what this all means, because you had sex, you know. No matter how planned or unplanned it was, that is what happened.
I urge you to visit a doctor or clinic and learn more about pregnancy and birth control before you accidentally slip in again.