Hi and welcome back to the world pollyvan9,
I know what you mean about not quite finished on a work. It is often my lot in life. I like your work so far and agree it still seems to need something more.
My first idea, and you may have already played with this one, is how about some more of those scrappy offset blocks to tie the piece together? I would place them in those 3 panels in an irregular manner I think. Play with making them a little smaller too perhaps. (I am assuming you might have some others that you made for this or another project?
Maybe just pinning 2 sides to keep them regular, or fold them in half and see what rectangles look like scattered in those large expanses?