If you're afraid of precum you should note that precum itself doesn't have any semen in it. HOWEVER, if there was remaining semen in his... shaft... the precum could wash it out, and that's how people get pregnant from precum. Basically, if a man has peed since last ejaculating, precum isn't much of a concern. (Still, don't ever risk it!)
But anyway it doesn't sound like you got pregnant given your story, there are plenty of other things that can cause a woman to be late.
Also, doesn't it take a few months for a pregnant woman to start not having her period? Might want to check into that and see if the timing is right.