I would add a border or two to the block. I would audition a green and a tan/brown similar to those in this block. If you decide to go with 2 borders, I'd consider a small white border,

I would notice (but, that's just me). The "Autumn Splendor" quilt that I did, had blocks that were not square. I averaged the difference and made my sashing strips that size. Stretching 1/8" will not change how the block lies.

Exactly what I would do!!!

This is what I had to do to conform all of my blocks from a soft book panel used to make a baby quilt. I also like the idea given about the matching (or close to it) white borders to extend the blocks.

I also agree with PP and ckcowl. The human eye and brain loves symmetry. When viewing your brain will perceive the border to be the same size all the way around. 1/4" will never be noticed unless you take a ruler to it. Cute block panel.

That is exactly what I did on a "not square" printed panel for a baby quilt. Worked out great and you can hardly tell the sashing is slightly different on the sides.

I'd just add a generous border and then square up to 12.5, very cute block.

I like the wonky block idea or you could add to two sides and make it an attic windows so it looks like the cat is looking out at you.

I wish this topic had came up sooner but still happy with my purchase. I am making a quilt for middle daughter that has blocks from 10"-12", I purchased the book Setting Solutions by Sharon Craig to learn how to make them all fit into her quilt. I should have known to come to "The Board" for suggestions, but all in all it's a good book to have for reference.
Jeri