How do I get her to back off?

Okay, so I just had my first kiss yesterday with this guy I really, really like. My cousin was hanging out with me afterwards, so I told her. But now, EVERYWHERE I go she's smiling at me and giggling. It's really annoying especially since I didn't want many people to know. She even told his troop leader (he's a former boy scout who was helping out with the cub scouts) "well we just wanted to thank you so much for bringing your cub scouts up here. My cousin here met her future hubby. Do you know *his name*?" How do I ask her to back off a little without being mean??