Vancouver is a city on the north bank of the Columbia River in the U.S. state of Washington and the county seat of Clark County.
The width of the twin quilt is 66 +12 (for the two extra columns of 9 patches) + 4 (for the two extra strips of sashing) =82, which is a bit wider than your target of 78, but close enough. Plus, it's nice to have it a bit too large than a bit too small.
You may add more blocks or borders for the drop (side) of your bed quilt. Not all mattresses are the same dimensions. But my chart will give you a really good idea of how many blocks you will need for these larger quilting projects. The size I will be talking about in this guide will be the DOUBLE or FULL quilt top. DOUBLE or FULL size (52 x 74).