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.
While twin XL is preferable (minimum length of 90), twin comforters and duvets (86 and up) can work on an 80 inch extra long twin mattress but they will be short. Please note that your mattress topper, fitted sheet, mattress pad, and bed skirt must be manufactured to properly fit a twin extra long mattress.