Semen After Ejaculation?

My boyfriend and I had sex the other evening. We used a spermicidally lubricated condom, and he came. We were careful to be sure of no spillage when he removed it. He wiped off a bit before we got to lying together and "fooling around" a bit more. At some point in playing, he entered me for just a moment or two, now without a condom. He withdrew quickly (and apologized!) when I said I was scared and didn't want to risk that...But what sort of statistics am I looking at for pregnancy?

What's causing me more stress is that I have an irregular period. The last time I had one was oct. 14, so I don't even know when I can go take a hpt, as they seem to say "one week after you miss your period."...But I was already a week late when the intercourse happened!

I feel stupid for being so worried about only a few seconds of my life, but it's consuming my every thought. I googled and came up with nothing on my own. I appreciate any input you all might have.