You lie and keep it yourself.

You tell her you didn't see anybody as you came in. She looks at you and says, "is anything wrong? You look nervous?"
You reply quickly, "it's because I'm not used to being so near a beautiful a women as you. Ma Cherie," you say in a cheesy French accent. She laughs and hit you with a towel.
"Oh be quiet you nut," She says. She has cute little dimple when she laughs. Its like her whole face lights up. She turns around looking for something to fix her hair with and you take a peak at her butt. You smile. She has a nice round ass. A lot of guys at school would kill to be with her. You really glad she agreed to come to the dance with you.
"You really do look beautiful you know," you tell her. She turns around and smiles. She has the prettiest eyes you have ever seen. It may seem cliched, but you feel that your heart went a flutter. "Thank you sweetie," she says. "So what do you have in store for us tonight," Katherine asks.
"Well you'll just have to see when the night is over. I like to keep you on your toes," you say in a joking manner.
"And maybe by the time the nights out, you may just get lucky," she says in a sultry playful voice.
"You mean I will win the lottery," you say joking.
She wraps her arms around you and gives you a kiss. Nothing X-rated but with a little bit of tongue. "You could say that. Let's go I'm ready"

You follow Katherine out of the bathroom and head down the stairs. Your heart skips a beat when you see her sister, now fully clothed, smiling at you with a smug look upon her face. She beckons Katherine over to her and whispers something in her ear. You can't make out a word that's said and can do nothing but look on hopelessly. You wonder desperately what she is saying to Katherine.