To start, this is an example of one of our "quilt as you go" blankets. This is block blanket one, which is the background for Forest Friends, Safari Shindig, Tricks and Treats, Gobble 'till ya Wobble, and Joy to the World. But the method is the same for any blanket that uses block blanket 2 or the building blocks pattern.
For the purposes of the tutorial we are going to focus on the three blocks that make up the center of the quilt:
First, you will attach the 2" piece of sashing to the yellow striped block using a 1/2" seam allowance. When you flip the sashing down it will hang out over the edge of the yellow striped block by 1". (There will be 1 1/2 inches of sashing showing but 1/2 inch of it is sitting on top of the seam allowance.) Next, you will lay the yellow and white striped block on top of the pink lattice block (with right sides together) and join them with a 1/2" seam allowance. When you flip the yellow striped block up the total height will be 26". Behind the 1" piece of sashing that is showing there is 1" worth of seam allowances. 1/2" from the pink lattice block and 1/2" from the yellow striped block. Thus, the blocks are actually butted up next to each other behind the sashing and there was no gain or loss in the respective heights of the original blocks.
Now there is no need to worry when attempting to join these two blocks to the 22" x 26" blue block using the 2" x 26" piece of sashing.
The same theory as above applies here. When you sew the sashing to the blue block with a 1/2" seam allowance the total width will increase by 1". Then, when you attach the yellow striped/pink lattice block with another 1/2" seam allowance the total width will be 37 inches.