If you can deal with the minor inconvenience of adjusting the wheel with the extra space between dropout and locknut, don't bother for now. Tightening the wheel with 3mm on both sides will not hurt anything. Trying to respace the dropout without the right tools will hurt it. If it really bothers you have it cold set at a framebuilder shop ie: Biseagal, Bike Specialties.
You can respace the hub to 126 as well. 2 3 mm spacers on each side of the hub axle.