Hi Peter -- if I may share my thoughts...
In general, Pages (SPPB) are displayed without main container (full with).
And all Articles has container (read more about it in Bootstrap documenation) that's why content is displayed at the middle with left & right space.
Without using extra CSS, you should be able to disable that container using Helix Template Options > Blog > Details > Full-width Layout: ON
whole rest request using extra CSS.
BTW
Try to focus on one component, for example SPPB for most pages, and Articles keep only for Blog, it may save you lots of time later in Google Search Console.