Losing my virginity

It was my birthday, 7th july. I woke up like a king, it felt like the earth was spinning around me. I organised a party with my friends for my birthday at 8pm and all of them came. We drank & smoked a lot and we were really fucked up. I had a girlfriend and we planned it out to have sex that night when the party is over. We both shaved, cleaned and all that. You could say we were prepared to have sex together. The problem is that my girlfriend had a twin sister and man fuck I was too high. I can’t explain my mistake, it was the dumbest shit ever. Just cuz of her twin sister I got confused and fucked her grandfather.