Basically, I am trying to design a basic 2D game/program as a test run through the code. There is a turret (I'm using a panel, but I believe a sprite would act in a similar manner) which I am trying to track the mouse cursor with (hence the rotational part). Using the "vec_to_angle" command, I was able to succeed in rotating the turret to track the cursor, but it doesn't rotate around the center of the turret, rather the top-left of the panel. By using,

Turret.center_y = Turret.size_y * .5;

I was able to shift the rotation point to being halfway down the panel. However, when I try to use
Turret.center_x = Turret.size_x * .5;

to move the center of rotation to the right, it has no discernible effect, even if I just set "Turret.center_y = Turret.size_y +500;" for testing purposes.
Sorry about the terminology swap, I's still getting used to it, but in this case I am specifically working with a panel in a 2D environment.