Sex With Best Friend

So my male best friend and I had sex and I'm on the IUD but it isn't in correctly and he didn't use a condom he came inside me, but please don't judge him and I are both in relationships he has his girlfriend and I have my fiancée we only had sex this one time because we both have feelings for each other, we both cheated but now I'm afraid I'll end up pregnant with his child because my IUD isn't in properly please help