how does the plan b pill work during ovulation!?

My husband and I had unprotected sex (condom broke) and ultimately came in my with no birth control. We didn't end up taking the plan b bill until 2 days later and the day we had sex was my most fertile day. So my question is: Plan B works to PREVENT ovulation. But if I was already most likely ovulating during my period of sexual activity, it seems like fertilization would have been inevitable. How affective will this Plan B be?