Greetings,
How can I force my web site to be full screen? When I created the home page, it defaults to a narrow center-aligned div. See image below.
Also, how can I get rid of the “Preside CMS” label at the top of the screen?
Preside itself does not really have an opinion on how the frontend layout is put together. The frontend will use the “Main” coldbox layout by default (see Layouts | ColdBox HMVC Documentation) and your page types will have their own views for rendering.
In addition, it may be worth checking out the Page layouts extension that gives you some more flexibility with defining sub-layouts for page types, etc. GitHub - pixl8/preside-ext-page-layouts: A general page layout framework for Preside
The default application skeleton (box preside new site) supplies a starting point for /layouts/main.cfm but it is then up to you to modify that and output whatever HTML you need/want for the frontend.
Following docs may also be helpful: Preside Documentation :: Working with page types