The most common cause of this is that the wheel axles are not fully seated in their notches at the end of the fork. The easiest way to get them to seat right is to loosen the wheel again, and install the wheel while the bike is upright and sitting on the wheels. Then tighten it up again and see if its right.

If not, then I would guess that the brake caliper needs to be readjusted. They do get knocked out of alignment sometimes. It is not a big deal to do this yourself, so let us know.

jim