You're calculating individual yards of fabric which makes you calculate too much. I came up with 18 yards for the background fabric. You would only be using 30 inches of fabric but have 6 inches waste leftover if you were using individual 1 yard pieces of fabric. I didn't calculate the window fabric but you are probably estimating too much there too. Although too much is way better than too little
-- more stash for another quilt!
I also noted that she used batting. I don't use batting in my cathedral quilts because they are heavy/warm enough without it. The batting probably helps to accentuate the window fabrics but depending on where you live, you may not want the extra weight/warmth of the batting. Just wanted to let you know that you can make one without the batting... Please post pics when you're done!
