I would add a row that mimic's the light portions of the previous row as close as possible, then add applique to the two corners and extend the applique into the previous row to hopefully balance it all out. I see that it is a print, so if you could match that print that would be ideal. If not ... try to match the white portion then work your applique in the darker color with small additions of red (for the cardinal) and green (to match the green in the center). Perhaps mimic the pine branch with pine cones from the center panel. I think I would make your border wider than the previous border to take the focus off of it.