Instead of waiting for the user to return to a page he’s not supposed to see and use a custom variable, you can overwrite the bookmark variable to make the user return to the Start page directly. Keep the action on each question page of the assessment but make it
Action: Modify variable
Of course you’ll have to update the value with the filename of the page that you want the users to be directed to.
Add a “Reset Test / Survey” action when this page is shown.