Corner Gas Fireplace - Core Catalog

[just3north]

I am trying to place the corner gas fireplace from the core catalog. When I place it within my wall on the corner, the front shows fine but the side shows drywall as if the wall was not cut out like the front. I have tried placing passthrough but now the program leaves a framing member in the corner no matter what I change. I am not familiar with how to open a wall at the end edge of the wall. Any suggestions?