It's then likely in your pages default settings file.
Make sure that Pages is not open.
go to ~/Library/Preferences
Find the file com.apple.iWork.Pages.plist (the word "iWork" may or may not be in the file name. The word Pages should be, and that's your primary goal

)
Drag that file to the trash, then empty the trash.
Now, launch Pages, and it should appear as first used, with no settings saved. Change your Pages to your liking, if you need to.
The Inspector pane, which is part of the document creation tools that you would use in Pages, should be at defaults. You MAY find that documents that are previously created, may continue to call up that Inspector. Outside of modifying the document file, there may not be much you can do, except toggle it off if you want. Saving a document in that Inspector-free state may be one way, but I think kind of "fiddly" for something that you can simply move out of your way when you don't need it.
I'm guessing you have a 13-inch screen or smaller? The small space could make that un-called Inspector annoying...