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.
A Twin by Any Other Name. A standard twin mattress is 39 inches wide and 75 inches long. Daybed, bunk bed or trundle bed mattresses in most cases are standard twin bed sizes. Some trundle bed frames come in full size as well; the mattress may be full or twin. If unsure, measure the mattress or frame. A twin or trundle mattress is not the same as a twin XL mattress, which is five inches longer and won't fit on a standard trundle or twin frame.