plan b

my boyfriend & i had sex a week ago. i’m not on bc so we always use condoms but it slipped off inside me & we didn’t realize until after he came inside me. it was the first day of my fertile window according to the app but i have really regular periods & i’ve been tracking my period on this app for years now. since i was a few days away from ovulation i took a plan b right away (within 30 mins) but i’ve read online that plan b might not be effective if you’re close to ovulation? is this true?