The walls don't make sense. I understood the first four rounds of wall creation, but the remainder doesn't make sense, nor does it fill up all the walls shown on the map you sent. Were there other walls previously created?
Also, the hole should be in the NW, right?
Attached is my rendition of the arena. Hopefully, my skillz in Excel will help with some of these problems. Note, first of all, that I'm using drawing objects and not borders for the walls an such. The O's are obviously Oromeax. The thick black line is the outline of the fog and the thin black line is the center point of the fog (I created various templates on another sheet, using the drawing objects, and grouped them so you can easily copy them and paste them on the grid; using snap-to-grid, it's easy to position the templates over the arena. You can bring-to-front anything that might be obscured by the grid.) The thick gray lines are the 20ft-high stone walls. The thick blue line is a 10ft high stone wall and the thick green line is a 20ft high wall missing the bottom 5ft. The southwest corner of the VZ has a gray rectangle over it (the cell is not colored) that is transparent.
Note that the default arena terrain is also composed of transparent rectangles. This helps because now I can just copy/paste the creatures without regards to the cell colors.