i don't think you have anything to worry about. when a man actually ejaculates into a woman the ejaculation forces the sperm up there to impregnate her so it is very unlikely that just a tiny bit of precum on your underwear would get you pregnant. even if you had a whole load of semen in your underwear it would still be very unlikely to cause a pregnancy.
gave a guy a hand job and touched a little precum. had to end it early so i put my underwear on a couple minutes later. okay so we had to cut it a bit short so nothing really happened. i just touched his precum. a couple minutes later i put my clothes back on and thennn my underwear with my hands that had precum. could i posssiibly maybe somehow get pregnant?