Concerned about missing period

Goodmorning lovely’s, or night wherever you are in this world. So a month ago;two days before my period i took One Step- plan B , because me and my boyfriend only used the withdrawal method. But, my period was normal and I got it on time two days later. I most recently had sex july 11th and we still did the withdrawal method however, i’m concerned that the pre cum could of had left over sperm in it, because we did more then one round. Or when he pulled out he came on my butt which could of dropped down to my vagina. I have missed my period by five days which could of been the plan B or i might be actually pregnant.

Please let me know if you’ve been in the same situation or if i should be concerned or not because i’m really not trying to get pregnant.