Hi Jeffrey!
It looks like the Full Width custom page template provided by the Post and Page Builder has some conflicting style rules with the Overlay theme installed on your website that are preventing that template from displaying as expected.
I installed that theme in one of my testing environments and I was able to fix these display issues with just a couple line of Custom CSS. I added my custom code to the Additional CSS area in the Customizer provided by the Overlay theme. Here is the code I used to get it working:
.site-container {
max-width: 100%;
}
.bg-custom-template {
width: 100%;
}
This is an example page I created with those custom rules to give you an idea of how it looks after making those modifications.
Hopefully these rules help you get the design you need on your website and please let us know if there is anything else that we can do to help!