Birth control change (dont know where to put this)

lex

So I switched birth control yesterday morning. I was on nexplanon. Got it removed and I'm now using the patch. I was only on nexplanon since January at my 6 week check up after having my son. So on nexplanon I know that my fiancee can cum in me and I wont get pregnant. The night before I got it change we had sex and he cummed in me. Should I be worried that I could end up pregnant through this switch. I know its possible but how likely?