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 typical twin size mattress is 38 x 75 so a twin comforter will be larger than this by several inches in both length and width. There is variety with different manufacturers, etc. King 110x 96 Twin and Full sizes in particular vary considerably in length and slightly in width.