i need some professional advice!!!

i had sex yesterday and we did anal but it accidentally slipped into my vagina where he wasn't wearing a condom. it was quick, in and out, because it was an accident. eve says my chance of pregnancy that day was 22%, but i didn't have discharge or anything that day so i'm not sure how correct eve was. my question is: how likely is it for me to get pregnant if there was precum on his penis when it slipped in? he didn't urinate beforehand either. is plan b necessary?