MissSongbird

I've been working on a quilting design for a quilt I am currently making and I think I know what I want to do but I need advice on how to execute it.

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For the border (the blue only) I was thinking of doing a diagonal grid pattern, like in the second picture but smaller. How is the easiest way to execute this? I'm worried about it coming out funny and like off center or just not a 'perfect' grid pattern.