Unprotected sex/period

I need some advice on this

I had unprotected sex last Tuesday and I went on Saturday to get a plan b at planned parenthood but I told the nurse I got my period on Friday and so she said I didn’t need a plan b, I took her advice but now I’m worried

I know it’s too late to take one now but has anyone been through this and has not gotten pregnant?? I have a 4 month old and I don’t want to get pregnant again