I think it's great and would call it done. Something to consider if you have a similar issue in the future: If I'm seeing correctly, not all the panels are that large and some have extra plain tshirt fabric to bring them to size. What I often do is make different sized rows. If some need that large a row, then I will have one row with large squares. That might be followed by a row of narrow squares where the design might only be 10 or 12". I don't feel like all the blocks have to be the same size in my quilts. If I have an extra single large block or 2, I might position them in the center of a row and use two smaller blocks on each side.
Just some things to think about if you don't want to deal with the extra length another time. I sure would leave this one as is tho, it's great and I'm sure it will be loved!