Write your mobile phone number on the note and give it to her. The content is: I like you. If you think I can make friends with you, please call the following number. If not, please throw it away.

The QQ number is also fine. If you can, please keep it or throw it away later.

This is more tactful and at least fewer people will know about it. Everyone will just wonder what you wrote, even if it is rejected. It wouldn’t be too embarrassing,