If it were me, I would add a row of the baloon fabric after the blue, then repeat the blue, then repeat the panel, facing the other direction. I'd use the rows of blocks like you have them, on each end under the panels. I would make the row of baloon fabric wider but not as wide as the panels. Perhaps 2/3s as wide.
I love your panel and coordinating fabrics! It's going to be a happy bright quilt.