Plan B while ovulating?

I was wondering if anyone has been in a similar situation as me and the outcome. I had sex Thursday morning and this morning. After having sex this morning I took an ovulation test which said I was at my peek for ovulation. I immediately went to the drug store and got the plan-b pill. So after taking the pill this morning that would mean I took it 78 hours after sex which is out side the 72 hour window which concerns me. Also everything I've read says that the pill prevents ovulation but doesn't stop it if you are already ovulating which also concerns me because of this mornings sex. Does anyone have some advise for me? I'm very worried I may become pregnant.