Running Windows in an emulator is not going to give you the exact same "look" as that of running it on bare metal. You are running it inside another app, and that app wants its own slice of the screen pie.
If you have issues with the way Parallels displays Windows, you need to talk to the Parallels developers. All Apple does is supply the compatible hardware and OS, 3rd party developers determine how their app works within that environment.
Everyone here is a volunteer and anyone familiar with your issue may or may not ever check in. For that reason alone, quizzing Parallels tech support is likely going to serve you better.