Issue with porpotional editing

I am trying to create a horizontal stabilizer after making the vertical stabilizer (horizontal wing on the rear wing of a a plane) and when I create the cut and try to expand it, the rest of the mesh moves with it.

Having turned off proportional editing, and all modifiers this problem still persists. Does anyone have a solution?

In edit mode, you can select vertices that you don’t want moved and hit “h” to hide them.

This dosen’t really help. The problem that I want to extend the face outwards without the rest of the body following

Perhaps these pictures may better illustrate my problem

Are you pressing E to extrude? Or just grabbing/moving the face?

Just grabbing it
Let me try

That worked

Thank you very much