Sex on last day of period with Nexplanon

My boyfriend and I had unprotected sex on the last day of my period and he came inside me. This is my second year with nexplanon so I am a little nervous that pregnancy is possible due to the fact that it is 99.9% effective the first year. I’ve tried to find the effective rates for the following years but I can’t anywhere. I have a regular cycle, so even if the sperm lived for 5 days it shouldn’t reach my ovulation day, but I’m still worried. Is it possible that I could be pregnant? Has this happened to anyone before?