It could be the printed pattern. I've heard that if you take and print a copy (say from a website) and then you use that copy to print another copy, the second copy will not be "exactly" the same size. Something about the fact that the printer reduces the second copy just a hair. So that being said, in order for all the copies to be exactly the same you would need to print all the copies from the main website that you originally printed the first one and not make copies of copies. I hope this makes sense. By the way, your block is beautiful!