There is surprisingly not any GUI option in Gnome 3 by default to change wallpaper settings. I use “dconf-editor” for this purpose. It is possible to center, scale, tile or stretch a wallpaper by using it.
“dconf-editor” can be found in the main repositories of Debian. Once you installed it, open dconf-editor, and navigate to: org -> gnome -> desktop -> background. There you will see the pop-up menu which lets you make arrangements on your wallpaper.