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.
Standard twin beds, also known as singles, hold mattresses that measure 39 inches wide by 75 inches long. Extra-long twins are 5 inches longer. Small children will fit this size of bed perfectly, but twin beds can accommodate adults, as well.