I hope you are well today and thank you for your question.
I have tested it on my test site by using a child theme of Unite theme which i have attached to this reply and found the pages are displaying full width for me if i select full width page template for them as shown in the attached screenshot.
You can make the shared pages full width by setting the full width page template for them as shown in the attached screenshot or you can make them full width by adding the following CSS code in the style.css file of your child theme.