Full width containers seem to be default for Sitejet without a simple click to box it. This seems to be the easiest way to achieve a boxed container and center it on the page. These are for the settings for the desktop viewpoint.
Hope this helps. Chime in if you have anything helpful…I’m all ears 
You can customize the width of a container in the container settings, see attachment.
Notice: Use percent or vw rather than pixels for spacing when you work with full width sections, so the spacing is flexible to the screen width.
Thanks @Dominik_Sitejet_Team! The percentage makes a big difference. I appreciate that! 