If you're doing the Trip Around the World quilt using tube quilting, you have to remove the final square on the bottom horizontal strip of the quilt in order to ensure that the bottom half of the quilt is symmetrical to the top half. The center horizontal and vertical strips are the only strips that do not get repeated. Thus, my quilt was 11 (3") blocks by 15 (3") blocks. The odd number accounts for the center strips.
Sorry I forgot to mention it while describing the construction of the quilt!