I slept with my friends father and i think something happened? kinda long!?

sorry if this is long but i just have to tell someone! last friday nite i went to spend the night at my friends house, my mom dropped me off and then left for the weekend for a church retreat. but i jad the date mixed up and my friend her mom were gone to visit her grandma overnight. it was raining so my friends dad let me in. he is always nice to me, so i didnt freak. anyway he said i can stay since i cant go home and be alone. we watched a movie and had popcorn. he sat right next to me on the sofa. then i went to bed. in the night a really bad storm started and i was really scared so i went in his room. he told me i could sleep with him so i did. i slept with my back to him and when i woke up later i could feel his thing on my behind! i had my undies on but still! i pretended i was asleep and then in the morning there was a crusty patch on my panties in the back. he was already up and when i went in the kitchen he was acting normal. i think i know what happened but feel creepy about it and wonder what i should do?