If the vehicle is brand new, wait awhile. It has been my experience that the fuel economy will improve with mileage until somewhere between 5k and 10k miles.
How are you measuring your fuel economy - on board fuel computer? If you are calculating it based on miles driven divided by fuel purchased, you need to calculate the average over a longer period. Single tank averages are notorioulsy inaccurate. It is my opinion that you need to calculate the average over at least 3 tank fulls (40 to 50 gallons).
The mileage you reported is a little less that reported in the Consumer Reports road test:
CR's overall mileage, mpg 19 CR's city/highway, mpg 12 / 28 CR's 150-mile trip, mpg 23
I'd suggest checking the odometer (against a measured mile, GPS, or a long run of Insterstate mile markers). Make sure the tires are at the correct pressure. Where are you located? Did you buy oxygenated fuel (E5 to E15) or some other "special" enviromental friendly blend?
Regards,
Ed White