Hi @ChrisBlanch,
I believe the only way confetti works with assignments is for "on-time" submissions, which means the assignment has to be turned in before the due date if there is one, or there would be no due date entered at all (which seems to be your case). In addition, your Canvas administrator has to have enabled the confetti feature or made it something you can enable in your course settings.
Hope this helps!
-Chris
