This has happened on 2 of my Curves, including my newest one. Basically the top-left corner of the phone is popping off, so much I slide a piece of paper underneath it.
I had the same problem after I replaced my lens. Idk if you'd want to do this... but you could try to slide a small piece of double sided tape in there? It helped for me but I had the entire lens off the device so it was easier for me.
There are several youtube videos that will help you with installation if you need it. It seems pretty simple to do, if you need a visual, might be helpful...