heellppp meee!!!

Ladies I'm freaking out!! I think about 6 days ago I was fooling around a bit with a guy! We didn't have a condom and I'd usually never ever have unprotected sex but I let in put it in for like 10 seconds! He thinks he didn't pre cum and is telling me not to worry about it but I can't help being worried :( can someone pleass tell me I'm being crazy or that I should worry.. I don't know what to do!