if u'r period doesn't come within 2weeks take a pregnancy test.. that's the way to go. 1% of the semen he ejaculated is sperm and the other 99% are all fluids.. and in that 1%.. half of that goes to the wrong fallopian tube.. so think about it what are the chances.. and he didn't even cum inside u it was just on the condom he accidently put on the wrong side.. there's no pre-cum cause he wasn't even aroused yet.. pre-cum will happen before ejaculation.. so the chances of u being pregnant is extremely low... mabye u'r period just missed all women has that due to many factors.. if u'r still worried take a pregnancy test at the doctors.. it's all confidential.. i think they would be happy to help