I make these all the time successfully but I use the cheat sheet from this site for my measurements:
https://catbirdquilts.wordpress.com/...h-cheat-sheet/
It never fails me. I printed it out and keep it in my folder of quilting hints and I also saved on my computer too. I have made Economy Blocks from 2.5 inches finished to 9 inches finished. My hint is to trim to square after each round being sure to leave the 1/4 inch seam allowance at each point. Give this another try. The economy block is so versatile
I just finished a baby quilt using the Economy Block last weekend.