TAKE PLAN B AND IM NOT PREGNANT

Dose anyone know what happens if you take plan b and you was never pregnant?? I’m just taking it just to be on the safe side I didn’t have sex but pre cum might had been in contact

Sb: it happened 2 days ago so I still have the 72 hours so should I just take it or not ???? I’ll prob end up taking it anyway but Is it going to mess up my cycle or something??