This should keep the upper and lower blocks very close to even.
First make sure blocks are the same size.
Using pins line up corners and every few inches along the area to be stitched. Leave these pins in vertically.
Next pin on either side of the vertical pins so nothing will shift.
Then pin across the line to be stitched, and you can sew over these pins if you would like
bottom side of blocks being matched, I would shift the bottom block so the corner matches better
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first vertical pins to match top line to bottom line
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put pins in on both sides of the vertical pin, do this beside all of your vertical pins, I would do the whole block.
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