Your quilt is beautiful! Im a little slow so I actually sketched four 9 patches and marked the diagonal lines.
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So....mirror imaged lines forms the center diamond. And just repeat the border around the center diamond. I get it!!!
Viewing ur post is timely as I have my 4.5 inch fabric squares cut for an I spy quilt. Was trying to come up w a plan to piece them. Your quilt Iis amazing. Thank u for posting.