I heard that pre cum can get you pregnant

Okay so I had sex for the first time and we had it unprotected. I know your not supposed to do that but we hadn't really planned to. So we had sex then he pulled out and came. I heard that pre cum can get you pregnant so I was wondering what the chances are for me being pregnant. It was three weeks ago and I don't feel different but I was supposed to get my period two weeks ago. It had never been regular but for the past two times it has been. What are the chances of me being pregnant