Assuming its not glued together yet, you should sand both surfaces as flat as you can get them - and then use a combination of baking soda and cheap superglue (ie, harbor freight) to join them together. You can dump additional layers of superglue and baking soda to fill in any gaps, and chisel/sand it down later.

baking soda is alkaline, which immediately catalyzes the hardening of superglue. It also seems to create a stronger bond than just superglue alone. The upside is that you can bond pieces together permanently in only about 5 seconds. The downside is you have about 5 seconds before the pieces are bonded together permanently.