1-2 mm equals about 1/16 of an inch, so assuming that all your strips lie flat to the forms and you don't take off too much material in planing and sanding, your boat will be about 1/8 inch wider and 1/8 inch less deep in the center than others of that design.

I doubt that my forms were even cut to a 1/16th inch tolerance since I used a hand-held sabre saw, so I wouldn't worry. Hopefully Nick will chime in with an authoratative answer shortly. Best of luck with your boat!