Howdy MarkK, My first two grows were the same way, tall and no bush! I added aluminum foil to the walls of My grow room (converted closet). It had white paint on the walls and I had read that that was sufficient for growing. Before the third grow, I added aluminum foil to the walls with plain old thumb tacks and wow! did it ever make a difference! Bouncing back all of the light towards the plants really made them bush out. I had also read that the foil could create 'hot' spots, but that never materialized and there has not been any damage to the plants at all. I could not tell what Your walls are made from or what type of lamp it is that You are using, but the addition of the foil is cheap, easy, and can be readily removed if needed.
Good luck with Your growing.