You can remove the outline of the rotating region by unchecking "Show Boundary/Outline" in the cut plot options.
I tried to replicate the other thing but don't get the same issue -
I'm using a reference plane rather than a surface for this cut plot - What are you actually selecting for your surface plot region? The rectangular cross section in your rotating region seems to be highlighted - I would double check your selections, or try again using reference geometry.
You're still able to do surface or cut plotting using excluded components, which allows you to plot pressure profiles across an orifice, for example.
Let me know how you get on.
that option did remove the border, but the isolines are still limited within the rotating region space.
I am using offset from the front plane as a cut plane.
I have uploaded the model with the simulation results (55MB file) here