just put mylar on the walls if you want to get the most out of your light and seeing how you will not be using near all the room you would probably be better off in a corner utilizing 2 existing walls and possibly putting up a temporary wall with mylar attached to it to reflect it back to the plants atleast on 3 sides of the grow area.
a 600 really only covers about 12 sq ft that would be about a 3 by 4 ft area.