Here are just two examples where I have had to use slightly wider size, red and navy strips, on top and bottom, framing up my panel to get my desired size. Then the extreme size difference, that was required on my America the Beautiful panel. I don't think I would fret about a 3 inch difference, Divided into top and bottom that's only 1.5 inch (2 in more if you have't included seam).
I have even had to add a different star fabric, on the sides, to make up my actual 'panel' . I was hesitant to do this but all my group said it wasn't something you focused on if you did notice. Good luck and show us your tops when you finish!