I am puzzled by the 'press them open'. I would be pressing the seams to the purple side. First, because it would be less visible and second, it would allow for nesting. But, I wouldn't cut until after pressing to aid in less chance of distortion (easier to move and handle a long piece rather than fiddly little pieces). I agree with cutting them a bit bigger. I learned long ago that the tiny bit of waste is so much better than ending up with a couple square too small!