I slept with a girl, shes my soon to be step sister?

About 2 months ago (jan) I meet a girl at a party, we got drunk and ended up sleeping together. Just the other day Onday to be certin my dad's fiance introduced me to her 2 daughters (both are y) turns out jess the girl I banged back in jan was on of them...how do I make it not so weird around her?? should I keep banging her