When I change the page width setting, it only respects it with the parent theme activated. With the child theme activated it does not work, it goes to full width.
Would you mind if I log in to your site and do quick troubleshooting? If this is ok then could you please temporarily create an admin user account and share the account login details privately by adding them in the box having text “Enter your private content here (only you and forum moderators will be able to see it)”?