So let me see if I can keep this straight anyway, we will see, if there is any questions feel free to ask them.
We are going to start with the trouble piece and get it out of the way, at least I hope so, line up the rectangle with one of the squares like this, and you can draw a diagonal line from one corner of the square to the other, make sure you get it going in the right direction or it will be backwards, which isn't a problem if you put some of the other pieces backwards as well, and when that is done, cut a 1/4 inch from the seam and press, ( I will leave you to decide what way you are pressing I pressed to one side, )
lined up
[ATTACH=CONFIG]61979[/ATTACH]
cutting off the extra
[ATTACH=CONFIG]61980[/ATTACH]
pressed open
[ATTACH=CONFIG]61981[/ATTACH]