The way to find out which is off is to draw a vertical centerline on the firewall and make that line 90 degrees to the workbench. If the fin is vertical and the stab is perpendicular to the fin then as Bingo Flyer said, it's the wing that's off.

If the fin and stab are perpendicular to each other but not square to the fuselage, then the airplane will always look like it's banked in one direction or the other if you square the wing to the stab. I'm not sure it would be worth cutting off the tail feathers though.