Hi Daniel,
So you are doing something wrong, but I don’t know what exactly.
Basically, what is happening is this:

From left to right, I to Inset, G,Z (blue arrow, if you want) to bring the smaller part doiwn and then E to Extrude that smaller part up again.
Practice that in a fresh Blender File with a simple Plane like this and when you got it working and understand what’s happening, Open your Press Start file and try it with the speakers.