Andrew,
> The room really only has two closed corners... see picture. <
I agree with Bryan that Visio is a great program for this type of drawing.
Is there any way you could rotate your setup so you face toward the right side of the drawing when seated? As it is now, with your head right in front of a reflecting wall, you have severe peaks and nulls across the entire spectrum from the lowest bass notes on up. Bass traps will help for sure, but having a wall right behind your heard requires additional treatment flat on that wall. Rotating your setup will also give better left-right symmetry which is important for good imaging.
--Ethan