judyisenhour, in general, "File -> Preferences" deals with the Scribus defaults - settings that will be applied to future documents - while "File -> Document Setup" deals with the current document. Changing the settings in "Preferences" will not usually have much effect on the current document (except in certain cases not relevant here).
Also, to change an individual page, rather than the whole document, you can use "Page -> Manage Page Properties".