I had to look for a while to see it.
Do you have any more of the border fabric that is around the images?
If you do, I would take out that square and reframe it. It looks to me like you could do partial seams to replace the unit.
Or take it apart, make the inner border a bit wider - which might be a bit noticeable, but maybe less noticeable? , recut the outer borders and put the unit back in the top.
After noticing it - which did take me a while to spot - it would bother me, too.