How good / creative are you at changing things around?
I see three options:
Buy it and then sew everything up (the squares, the middle, etc.) and buy extra white fabric and see how you can rearrange things to make it more narrow and longer before sewing it all together
Another option is to buy two of them LOL and have the center piece centered, and have a rectangular inner border, then the outer border.
Final option ... buy the pattern only, and adjust it to how you want to do it, and then buy your own fabric
If you have EQ you could design it (lots of us on here have it - I do) and could show you what it would look like.
I'd be willing to try and show you what it could look like if you gave me some ideas on how you would like the layout!