Sex + period + Plan B

So was having amazing sex with my husband and I'm on the pill but I forgot my period is suppose to start in the next day so I'm currently on the placebo pills this week (took the last blue pill this previous Saturday) and let him cum inside me and realized all this when it was too late. Since I know I can still get pregnant while on my period and I understand the Plan B can effect your period, what risks are there if I were to take it? I tried searching it and all it said was that it could cause my period to come early or late but not if I'm ALREADY on it...