Hi Beebythesea, and welcome to the forum.
Where I think you might be running into trouble is thinking that the style sheets are the same settings as Scrivener’s default formatting in new documents.
For the defaults used with each new document created, you’ll want to review the settings in File > Options > Editing > Formatting. The settings used there will affect all text used in all new documents. And, it will also affect every Scrivener project.
For project-specific formatting, you’ll go to Project > Project Settings > Formatting and tick the box next to “Use different formatting for new documents in this project.”
These two options will only apply to new documents going forward. To apply those settings to existing documents, you can use the Documents > Convert > Text to Default Formatting command.
That command can be destructive, so I suggest duplicating a document and testing it first.
Another option for changing the global defaults is to use the formatting bar in the Scrivener main editor, select the text that has the formatting you’re using, and select the Format > Make Formatting Default command.
None of these above options are using Scrivener’s Styles, and there’s a reason for that.
In Scrivener, the default “No Style” is the equivalent of a “Body Style” in a true-word processing program like MS Word. When users are just getting starting with Scrivener, I’ll typically recommend that they leave most of the text using the “No Style” default and only use stylesheets for exceptions to the defaults like a block quote or quoting poetry or song lyrics in a prose document.
The reason I recommend that is it allows Scrivener’s compile tools to have the maximum amount of flexibility when compiling the text to different output file types.
And, that’s one of the keys about using Scrivener. The text in the main editor can be styled for the user’s writing comfort, and all of those settings can be changed by the compile tools to match submissions standards.
For my work, I’ll use different fonts and font colors for each round of revisions and the “No Style” default. Then, I can compile to Manuscript Courier or whatever I need for the output file.
Does that help explain the behavior you’re seeing and which settings you’ll need to change?