I would definitely try to use more of the vertical space since it is so narrow.
You can either use bigger rocks or make a pile of rocks to increase the vertical range of the hardscape. The rockscape you have now is a little bland and lacks drama. If you had more of them you could make some caves etc...also getting similar rocks will make it less distracting.
Driftwood could also be great for using the entire height of the tank. You could have big sticks descending down to look like submerged roots, or you could do a tree stump scape.