GSX doesn't have any control where the jetway goes, that was only possible in P3D, where jetways are controlled by SODE.
In MSFS, there's no SODE, and jetways use the default animation system of the simulator, that doesn't know anything about your customizations in GSX, so jetways dock on the first door they find, and nothing you do in GSX will affect that, because it's the simulator itself that decides where to dock the jetway, and add-ons can't ask to dock to a different door.