When you do a swap in particular, but with any project where a consistent width or length is critical, the easiest way to assure that your row is long enough without being too long is to end the right and left end sections [or top and bottom depending on direction of row]with some extra length. This is easiest when you have a solid, not a pieced section at the far ends. This way you can measure the section you are attaching to and without stretching, lay out and pin your row. It is easier to remove than to add. I have also done this with triangle pieces, cutting the end sections just a little longer. It looks better to have a triangle point "floating" than to have it cut off.
I am trying to make my blocks. I thought I worked out all the measurements and it still comes out short. I still may be 1/4" short. Oh my, I have so much trouble figuring the measurements.
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