My first question is how did his penis "accidentally" slip into you? Was he walking by and slipped and fell *into* you?

Anyways, how old are you? Your cycles normally do not regulate themselves until you are into your 20's. Before then it is difficult to tell if you are a day or two late, as it would be expected for your cycles to very slightly on a monthly basis.

Due to the situation that you described I would *highly* doubt that you became pregnant. However, if you are worried, then you can do a home pregnancy test.

If you decide to continue having sexual relations, then you need to get on a reliable form of birth control. And make your partner wear a condom.