If the headline was a bit confusing, this is what I mean:
I copied text from one Scrivener project and pasted it into another (Scrivener project).
In the original the text filled the whole writing column / writing area. But once it was pasted into the new project, it turned into a much narrower “column”, only filling half of the width of the writing area. And I don’t know how to spread the text to fill the whole writing area in the new project.
Any advice how to spread the copy pasted text?
Instead of Paste, copy it in as Paste and Match Style.
Also look at the ruler (stop hiding it if it is not shown) to get an idea of what the parameters of the pasted paragraph are - margins etc.
If all you want is for the pasted stuff to match your usual default formatting, you can Document - Convert - document formatting to default style. This will change everything but if everything else is already your default style only the pasted paragraph will change.
You can also create a paragraph style and apply it to the pasted material; if you generally use one of the preset paragraph styles just use one of them.