Hello John,
Your homepage is still using the default page template. If you switch to Blank - No Container | Header, Footer, the sections, with the background colored blue, should be from on the left to the right edge of your browser. If you want, I can create a demo for you. We just need your WP Access details. You can create a secure note in your next reply with the following info:
– Link to your site
– WP login URL
– WP username
– WP password
– WP Administrator Role
– Confirmation that we can access and make changes to your site
To know how to create a secure note, please check this out: How The Forum Works

As for the child theme, if you are modifying template PHP files, or adding custom CSS styles and javascript files, it would highly be recommended to have a child theme.
Best Regards.