Im thinking it would alright to make a plastic veneer to go over the panel, something shaped appropriately in cad, printed filled sanded and then adhered to the original surface.
i know nothing about cars but i imagine you could take the panel off completely and once the veneer is in place fill in from behind with bodyfiller in case additional structural integrity is needed. the entire surface would then have a thin layer over the top hiding the cracks and cover the gaping hole. i would imagine that would be coverable in vinyl.
i guess alternatively you could print a smaller print about the size of the hole with the correct curvature, pack in and fill the back of the original panel and then pull off the 3d print. i would suspect then adding a thin layer of filler and sanding it flush would be trivial.
Might want to research compatability with vinyl wrap as to what itll adhere too.
additional information hides here
on your pc install https://alicevision.org/#meshroom
i would grab a white board erasable pen or similar and draw patterns over the white panel, then take loads of pictures with my phone in all angles i could think of. usually more photos provide a better result.
then use meshroom to extract the 3d features out of the photos, then import into your 3D cad program for filling in the hole by adding a curved surface and constraining it to the original shape around the edge… then slice it up to fit your print bed.
depending what you print with, say if it is in ABS, you get acetone mixed in with some spare ABS filament to create a glue for recombining the seperate pieces.
if you print in abs you can also use acetone to smooth the layer lines out of the print, to probably give you a fairly convincing smooth paintjob.
(if you have any trouble with filling in the curve send me the scanned mesh and I’ll fix it up)
^ i tucked away info on the software needed and steps etc in that drop down.