Will plan B work??

I had unprotected sex yesterday and the night prior. Semen did enter my vagina multiple times. I took plan b hours later (about 8 hours our initial encounter). I wanted to know how effective it is during fertile days. The last few days according to this app claim that my risk for pregnancy was high (about 20-30%). So I’m curious to know how fertile days are affected by this drug if they even are going to react differently