GSX, by default, will *suggest* to install into all the supported simulators it finds installed but, on that page, you are supposed to check which ones you want to install into, and will wait for your confirmation before proceeding.
If you realized you made a mistake, and want to reinstall into different simulators you originally chose, Uninstall it and then Reinstall it, and uncheck the simulators you don't want to install into.
did not want it installed in P3Dv4 as I want this sim for complex aircraft only and not GSX or scenery etc
GSX is designed to be used with complex aircraft, and it works so much better in P3D4, that I would expect you would do the opposite, and not install into FSX...so please, before doing that, try it in P3D4.