I agree that adding piecing into the border would be nice because it would continue the design all the way out to the edge. I thought maybe a triple border would look nice with a thin (1-1.5") white inner border with cornerstones, followed by roughly the same size or a bit larger of the green striped fabric you used & then a much larger border of grey fabric(s) with alternating blue & green squares on point. I know that's more work (sorry!) but your quilt looks so lovely I thought it deserves to be beautiful all the way out to the very edge.
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