Should I get Plan B or would it be a waste?

I had unprotected sex and he finished inside me. I was going to get a plan B this morning however I remembered hearing that it doesn’t work while you’re ovulating so I went to check the Flo app and according to it I am ovulating. I was reading on here and people are saying that apps aren’t reliable to track ovulation at all, so should I ignore it and get the plan B anyways or would it just be a waste of money? And if I am actually ovulating am I completely screwed or is there anything I can do to prevent pregnancy?

(I know plan B isnt BC but I felt like I’d be more likely to get a response on this sub)