I just got a new 2010 Accord and I love it but the gas milege is NOTHING what they said it would be.?

I get only 250 miles on full tank of gas(18.5 GAL) Manifacture milege is 21mpg city and 31mpg freeway.Should I take my car back to dealer to inspect or just forget about it? Btw my car is 4 cyl.