Xara Page & Layout Designer 11---Desperately need help on one issue

[letsgofishing]

Not sure why you want to reduce your page size to the size of the coupon.
I would make your page 8.5x11 and then using the guides, place on horizontally 1/2 way down the page and 1 vertically halfway along the page.
Then create your voucher in the top left quadrant (allowing for any bleed) and when finished, right click and drag it to the remaining 3 quadrants.