Pregnancy on Last Day of Period?

Nicole
Hello, 
I am looking for some insight if anyone has got pregnant on the last day of their period. 
My cycle averages 24-25 days. My boyfriend and I had unprotected sex on Friday, March 11th (closer to early Saturday morning on March 12th), where he ejaculated inside of me without a condom. My period was over and I only had some dark brown discharge. 
We did not take Plan B because we thought I wouldn't be fertile for a few more days however, I am reading online that Sperm can live for up to 5 days which would take me near my ovulation date. It is too late to take Plan B now because the 72 hour window has lapsed. 
Does anyone have any insight if they have been or heard of a simile situation as mine? We are both a little nervous right now. 
Thank you!