I kept sewing until I joined all the 6" blocks together, creating the quilt top in thirds.
Then, I pinned each third to its corresponding side and sewed them together.
I broke my rule... I ended up ripping the seams out of the quilt thirds at least 3 times and in the end, I had to let some of the mismatched seams slip. It is harder to match up 6 seams than 1 or 2. Either way, I wanted it to be perfect and it wasn't but I am just looking at it as "character."