So here's my tuppence worth: the first unit you put together looks like this, with the seam pressed towards the darker fabric:
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(Sorry about the shadows but I have to have lights on here this morning as it is so dark, windy and rainy.
(For a change.)
When you join these two blocks together my reading of the instructions suggests that you press the centre seam open, like the one in the left of this photo. I chose to iron the seams to one side as on the right of the photo and as Laura did in the demo because that means that when you are putting the four blocks together the corner seams nest together much more smoothly.
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The next step was to sew these units into fours (it would have been good if the instructions could have told us to trim them to 3 1/2". I had to go back to the demo to confirm it.) I also found squaring up these QSTs with the X perfectly centered was not that easy. Then the decision was whether to press open or press to one side. I couldn't decide so I did one of each to see if it made any difference. It didn't seem to make any difference to the finished block.
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Seams open on the left block and seams swirled in the right block.