Gangbang Pt 2

If you haven't read Gangbang, I highly recommend it. It's about a woman who goes to a party, meets a man, and agrees to have sex with him in order to prove she's a good girl. As she's doing it, she realizes she likes it, and then is told she has to do more than one guy. She agrees, but when she's forced to have sex with a stranger, she has a panic attack and escapes.