That's a good call. To separate the possible causes I'd unclamp the cable and see if the derailleur will push itself out to the smallest cog on it's own. If not then I'd say it's warranty time.

And just to eliminate all the possibilities check that the hanger is as straight as your eye can detect. From there if your shifter cable is not a full coverage cable then check that each section of housing is easy moving. With the cable disconnected you can even draw out the section at the shifter a little and check that section too. If there's anything but easy movement in all sections then either fix it yourself or take it in for them to fix.