PLAN B .. PANICKING

A few weeks ago my boyfriend and i had unprotected sex & he accidentally pulled out while he finished inside of me. Minutes later we went and bought plan B. I experienced all of the side effects  of the pill now i'm 3 days away from when my period is supposed to start and i'm having my normal pre period discharge , cramps and Pms. i'm still worried and i know the second my period is late i will begin to panic . Help. Will i be okay ? how late can my period be ?