Creampie! StepSister watched!

I was freshened up in the bathroom at lunchtime because the three of us all wanted to go out again. The friend of my sis wanted to go to the bathroom again and stretched through a crack in the door .. that made him somehow horny, so that he suddenly opened the door and presented his cock. I liked what I saw, but hesitated .. because it was after all the friend of my sis .. but horny as I was, I just took the big stick deep into my mouth .. then I willingly stuck my ass out and he fucked deep inside my hole .. I rode the horny part then also .. He then inject all his sperm deep into me .. it ran extremely out of me, because he had a really full load. As he was pulling his cock out of me, suddenly my sis came around the corner! She caught us freezing !! What should I do now??!