Let's apply some pressure...

"Yes, I found it", you reply and take a step towards her.
"I had to look inside, of course", you add.

She blushes. Whatever she uses those two dozen ballgags for - it's not something she wants the world to know.

"I thought it belonged to you, but I wasn't sure, so I thought I drop it here, but I also took pictures of the whole content and wanted to hang them on the message board downstairs, so that if you're not the owner, they can recognize it and come and claim the backpack. It's alright if I scribble your roomnumber next to it, right?"

Her eyes go wide, her cheeks turn into an even darker shade of red. The look on her face tells you that she's not sure if you are joking or serious. And that there's a fight inside her about whether to call your bluff or not. You try to keep your face straight, although it's hard.

"Don't", she finally says, hoarsly.
"Sorry?", you ask.
"It's mine. You were right. Can I - can I please have those pictures?"
"Why", you flash her an innocent smile.

She bites her lip.
"How about...?", you walk towards her and grab the backpack, which is still lying on the floor, "... you let me inside, answer me a few questions, and then I hand you those pictures."

She looks at you, her face a mixture of fear, misery and hope, that this will all turn out well.

"Alright", she finally says, and bids you inside. It's hard to hide your grin. She's yours, it seems. You walk into her room, which looks as pink and hellokittyish as you had expected, and sit on her bed, taking control of the room and the situation.