Custom Made Wood Frame 2.5” X 2.5”

I had this specially made for a small drawing I had that I wanted behind glass. There is a slight gap between pieces of wood, see corner photo. It’s really not noticeable when on the wall, but it must be disclosed. I’m not sure how to fix it, but I’m sure it can be. The pieces are not lose so there is no rattling, it’s a solid frame.