I just realized I can't count
I was using an 8 x 8 grid, not a 7 x 7 one. Duh!

Looks like there is more than one way to make this.

It is called "Ceiling Tiles" by Amy Garro.
http://www.quiltingmod.com/2015/03/q...ds-part-i.html
https://www.13spools.com/blog/2015/0...ed-modern.html
https://www.thecottoncupboard.com/mo.../ceiling-tiles
https://staceyinstitches.com/tag/amy-garro/

I drew this up in EQ, but see Janey has found the pattern so have deleted mine.

Thanks so much! Even though I drew out the pattern I'd like to see how it was originally done so I just ordered the book from an Etsy seller!

Here is what I came up with
https://www.quiltingboard.com/attach...1&d=1718853208

Brilliant idea to do the design in the sashing!