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.
If you have two twin sized beds, the minimum size of the bedroom increases up to 9 by 9 feet. The standard size for bedrooms with two twin beds is a bit bigger at around 10 feet by 10 feet. The minimum size for a room that has a double size bed is around 9 feet and 6 inches by 10 feet and 6 inches.