First of all I see you have less than 400 miles on your car so there are several questions to ask.

Did you fill up immediately after you purchased the car and reset the milage gage? Do you know that the dealer filled it completely when you purchased it? Have you ever reset (assuming you have NAV) the trip milage to see what's going on currently? Things like this can really mess up your initial tank milage. I'd fill up now and start monitoring it and then let us know what type of driving you're doing and the milage you're getting.