Because the cut was on the bias, it will stretch differently, or shrink in the wash and not all sides will do so equally. So the instructions say to keep the top and bottom and side pieces on the origianal way before cutting. By marking it with pins and lettering the back side with a top, right, bottom, and left there are no mystery on original placements. I also have stay stitched before cutting the 'x' across the square. That helps, too. Have two more almost ready to put together this morning. Hope that answered the question, Givio. Interfacing or bias seam tape could be appplied before cutting on the bias 'x' so it would not stretch, also...before getting it seam together.
Have a great day.