The GSX menu is not something we have any control over.
It's the standard Simconnect in-game menu, which is shared between all 3rd party addons using such menu. It's created by the sim itself, and no addon has any control on its size and position. You must have resized it manually. We have noticed that, sometimes, the size of the menu changes when using a PMDG airplane so, maybe they found a way (or use some kind of hack) to control its appearance, but surely we don't, so this is entirely unrelated to GSX.
You should be able to right-click on it to undock it so, once it's undocked, it might be easier to resize it and then dock it again.