Mods are limited as to where they can place GUI items. "Top", "Left" and "Center", and unlike base game GUIs, they are not movable. So if you set it to centered, it covers the base game GUI and therefore you can't use the base game GUI while this is open.
Check the options, it should apear on the left ONLY if you have the option set to dual mode, and centered if you don't. if this is not the case, let me know.
Dual mode is the one that opens when you click an inserter, standard mode when you point and press E.