I figured it out!!
I tried to work out the math with my 17-year old wizz, but we got hopelessly confused!
Instead, I took rotary cutter to fabric, and after much trial and error-well, error-we got a version we like.
It’s not going to be the whole quilt, it’s just the focal point.
And as always, no comments about my lost points are necessary. I know they’re there 🤦♀️