If your average trip is short and in cold weather, the engine naturally burns more fuel to warm up (running rich) until normal operating temperatures are reached. You will also notice the higher RPMs when its cold as it works to warm up, therefore burning up more fuel.
I have religiously monitored the MPG since new. I have 65,000 miles now. Luckily I don't have very much cold mornings over here, therefore it warms up quickly and reaches normal operating temperatures in no time.
My logs show constant 26-30 MPG every time I fill up. I take the miles driven, reset the trip odometer to 0 and divide the miles by the number of gallons used after I top it off at the pump. Rinse and Repeat at every fill up.
On long trips, ONLY if I drive a constant 55 MPH, I would get close to 380-400 miles per tank which upon fill up, it would calculate out close to 32 miles per gallon! But it is dreadful driving at 55 when the big trucks pass you by at 75! The only situations I would be able to cruise at 55 is on a busy highway (mostly holidays where everybody is on the road) and everybody is cruising along around 60. These are the only few rare instances I have reached close to 31-32 MPG, Memorial Day weekend, Labor Day weekend, 4th of July weekend trips with congested highways. But it is good to know that if I keep it at 55 MPH I would get close to 32 MPG.
But most of my daily highway driving is around 70-80 MPH and I get about 28 mlles per gallon. On weeks where I do heavy city driving I have seen it dip to 24-26 MPG. Overall I am pretty happy with the MPG I am getting. I have never gotten less than 24.
If you are doing mostly very short city drives with a cold engine, getting 16 or 13 MPG maybe the norm.
Take a weekend trip out of town, fill it up, reset the trip odometer to 0, and see what you get on the open road when you fill it back up at the end of your trip and calculate it out. If it is within reasonable range 24-28 then everything is good. If you still get lousy MPG, I would take it back to the dealer since it is a new vehicle and something may be out of spec.
Good Luck !