Assuming that the rotor is bolted in to the hub correctly, this sounds like your rotor is slightly warped, this can affect any rotor; you can get specific tools, like the Park DT-2 http://www.parktool.com/product/rotor-truing-fork-dt-2 to adjust rotors, of alternatively, use an adjustable/crescent wrench.

Being as it's only 6 months old, taking it back to Dicks, and asking them to swap the rotor for a new one may be worth a try.