Well, the white box you are referring to is the content area. Any builder (be it SiteOrigin, Beaver, Visual Composer, Elementor, Divi, Pootle, Rocket Builder or some other) will work only on content-area.
Now different themes have different layouts ofr content-area.
Some have a full-width content-area. Some have a right-sidebar-left-content area layout. Some have a left-sidebar–right-
The theme you are using has only one layout for content-area. Everything you build will have to be build on that area only.
One thing you could do tommake the page look full-ish is to use widgets in your sidebar..this is missing from your website.