Having the squares separate allows for errors and also to arrange them in a specific sequence. You can draw the seam line, but there's no way that you can be sure that some folks will just ignore it. In my paper business, I worked with an event planner who had some horror stories of guests signing a single item, usually someone who thinks inappropriate comments are funny.
A good way to work this is have someone who understands what needs to be done monitor the table where the activity will occur. Seems like there's always an auntie who wants to help with something, or maybe a couple teens who want to be included.