Aww come on now, that turned out quite decent!
And its important to not filling images with everything under the sun, give the eye some resting space, I would say that you actually obeyed the thirds system with this layout.
If you want to put in a little more, maybe just cut a doorway onto the wall on the far right of the image, like show that a hallway is there or something, that is the only spot that looks unused.
Maybe try pumping up the light cast in by the window on a separate layer, like the sun is just coming up and it is throwing a hard beam into the room. That might be fun.
Its a fun image that shows you nailed the perspective.