Closure?

[chrissidoll.livejournal.com]

I just made this little purse out of old material I snagged from my high school's color guard flag boxes:) It's a going away/graduation gift for my best friend. It's about 5x5 and I noticed that it sags open in the middle a bit when I hold it.

I've sewn it all up and I like the way it looks, but I was just wondering if anyone has any ideas on how I could make a closure at the top...or if I should just leave it.