Not really viable for a front wing but when I did my front spoiler all those years ago a papier mache mould made the fitting easy.

In this case I think I would get some stiff card from an art shop and make a simple template to fit the body.Then transfer the template to the wing but deliberately leaving an extra inch.

Then trial fit and slowly remove the edge until it's right.

DaveW
'05 Red Roadster S1
'16 Yellow (Not the only) Narrow AR GDI Plus 4