If it doesn't bother your feet/knees/ankles/whatever? Sure, you're done.

There are expensive options (phil, etc...) that offer offset spindles. Some other brands of bottom bracket may allow the use of spacers on the right hand side, with a left retaining cup that lacks a shoulder. 3mm is quite a bit of spacer for a bottom bracket, but as long as you have adequate thread engagement, you should be fine. I've personally done this to space a bottom bracket for use with an odd freewheel, but is not something that I would undertake for a customer without express understanding that there are better (but much more expensive) solutions.