Okay, I just learned why it is not a good idea to join the strips in sets then join them together as a whole. I did the first 9 stips one at a time. Then, I did the next 10 stips together one at a time. When I joined the two pieces together, I tried really hard to match the seams correctly (the seam on the open edge has to match the seam that is one row in so you can't just match two open seams together). I pinned then looked and it didn't seem like a good match so I repositioned the fabric and pinned again. After sewing it and removing the pins, I am off by about 1/8 or a little more. You basically have to use a ruler to to tell but it is still very frustrating.
I will follow the original directions for the top half of the quilt and just keep adding one more vertical strip at a time. I did not press as I went on the bottom half so I will not press as I go for the top half to keep them consistent. I think doing the pressing is going to be hard on such a large item with so many seams to press at one time and so close together. I am worried fabric will get trapped in the seams since you have to press from the back side. I guess I'll see tomorrow when I get to that point.