Choose a 'landscape' orientation for your single page.
Place a temporary vertical line from top to bottom edges of the page anywhere on the page, then move it to the centre of the page. ock the line to prevent accidental movement.
Place the elements of your invitation on the left side of the page. When you are happy with the text, graphics, and layout of that invitation, Select all of the items (not including the line down the centre of the page), then go to the Arrange menu and choose Group.
Copy the grouped objects, then paste them in the right side of the page, and adjust their location as needed.
OR
With all objects of the invitation grouped, Press and hold the option key, click on any of the objects, and with the option key still pressed, drag a copy of the invitation to the right side of the page.
Before printing, replace the line down the centre of the page with two tiny dots, one at at or near the top of the page, the other near the bottom of the page, and both centred on the division line.
Unlock and delete the line. Use the two dots to place the sheet on a paper cutter with the two dots aligned to thecutting line (edge of the cutter's platform).
Regards,
Barry
PS: Staples will likely be able to cut the cardstock for you without requiring that two dot marker for the position of the cut line.
B.