No sex but could still be pregnant?

My boyfriend and I have decided not to have sex because of how paranoid I get about getting pregnant. This weekend things heated up and we undressed and his penis was rubbing on my clit bare. It wasn't for very long, and he didn't cum. I was also on the first day of my period, and was wearing a tampon. 
I don't know if there was any precum. It was rather dry- which is why we stopped, so I personally don't feel like there was any precum. 
I cleaned myself off immediately after and changed my tampon. 
He had just gotten out of the shower, so I don't think it would be possible that there would be any dried cum residue on his penis.