Period sex with mirena iud

Hi girls I was wondering( I'm not panicking) as of right now but I did have period sex with my boyfriend today I'm on my second day of my period, and I'm also on the mirena iud, I know it's rare to get pregnant but do you guys know the chances of me getting pregnant?? I mean I've been in it for a year now I'm one of the few who still get a period and my period last about a week still so idk should I take plan b or not worry? He did cum in me for the first time he usually pulls out but this time I let him finish in me, help!