Precum touched my vagina but i took plan b 24 hours later and i got my period at the regular time but it was shorter, could i still be pregnant?

Pregnancy unlikely: Plan B can alter the menstrual bleeding for the cycle in which Plan B was taken, and sometimes the next cycle too. One should be sure to check a home pregnancy test about 3 weeks after sex, because Plan B works most of the time, but not all the time. Home pregnancy tests are sold in stores everywhere, and are fairly cheap to buy.