Don't give up!
It gets frustrating at times specially after you spent a lot of time arranging the rocks and wake up the next morning and realize you don't like it after all :)
For me, I find that it helps to sketch things out on paper first. Since you have a cube, try to sketch the representation of the front, left, and right views.
Here's a trick to help with rockwork:
You can use PVC pipes and plastic "egg crates" to act as the frame for your rocks. This gives you a design advantage in that you can crate a facade of live rock on the visible sections of the tank, but the interior is hollow.
You can also incorporate egg crate ledges where you can place live rocks and corals. Arrange it in a way that the plastic materials are hidden from view or at least do not stand out visibly.
This will also create the illusion that you have a larger rockscape without the associated weight. It also gives you the added feature of large hiding spaces for your critters "behind the curtains".
** Just make sure you have a small powerhead in there to keep the water moving.
Or design the rockwork so that the detritus do not funnel into and remain in the said hollow space.
Think of the typical frag racks, but make the shape more organic or at least more randomly staggered.
Post a picture of your current rockwork and we can throw out some suggestions.
