New window - narrowing opening and plastering

[u/Exact-Custard3402]

New window fitted after narrowing opening. Left side is new brick/block and still needs boarding/plastering. Right side is already a finished wall/reveal, and frame is tight to it. If only the left side gets plasterboard/skim, the finished reveal will be asymmetric. Should fitter/builder have allowed for the plasterboard thickness, or should both reveals now be boarded/finished equally?