Take the green away. You can either now use the outside of the cut out as a guide for the paper or as I did I looked at the mat where the image has just scratched the outline of the envelope and place the paper. I will draw some lines with a permanent pen to show me where I place the paper for next time, not across the whole mat, just the very top and the side bits where it is not sticky.
Now you need to cut the side that are overlapping away. I very crudely did it in the next picture and I stuck the mat in the machine.
Now remember to tell your machine you have 12 x 24 mat in there and let it assume there is a full sheet of paper. FIT TO PAGE, ROLY POLY. and you will get a 6 x 6 or very close (slightly bigger) envelope.
Thanks to Paula for experimenting with, I would have never thought to do this but am so pleased she did as 6x6 is my preferred card size. BTW Paula your directions home were fab, lot more straight forward than they way I got there!! :0) Hope the boys didnt leave you with too much tidying and WOW your studio is lovely, no scrap that, your house is lovely!