What are the statistics of getting pregnant without sex?

(I’m also on the combo pill) My bf went down on me the other day while I was laying down on my back and he was also jerking himself off the the process. There was a towel under him and he told me his cum went on the towel. But I overthink and fear it could have gotten on my vagina or vulva. But what are the chances his cum got on my vagina even though his face was covering my vulva? No hate please