Well, if you make a template out of ply to the shape of the curve.........by making a cardboard one first cutting this one with scissors,then transfer to the ply one .......you can run that across the face of the patch.....I would then bulk out the hole with a lightweight plaster like bonding or hardwall...running it with your template ...........then smooth with multi-finish plaster or Easi-Fill which is the joint finish for drywall . that`s what I`d do
and did similar on a smaller scale to a curved wall/ceiling Hth.