Mine started doing that & initially it wasn't so bad. I just had to push down a little more firmly to make it close.
Eventually, that progressed to where I had to push it down 3-4 times in order to get it to actually close. Also, there were times when I thought it was closed and after a short time (a few minutes), it would pop open again.
I eventually took it to the Apple Store & it was sent in for repairs.
They ended up replacing the entire display! Thankfully, all covered under warranty.
I would say if you're having this problem & it isn't too much hassle to do, consider taking it to your local Apple Store for them to look at. Of course, you'll have to be prepared to be without your baby for a week or so.
Don't forget to back up your data if you do take it in!!!
Good luck!