welcome to the forum. engine needs to be broken in. also are these city or hwy miles, are you using your air condition all the time, are your tires up at 32-36 psi. are you doing a lot of idle running. drive it over 500 miles than take another reading. it should improve.

 

The wild guesstimator is often off a bit from real world. Ciphering after a fill up is the only real indicator. Also, is this the first tank since you bought it? Dealers will let cars idle while they are doing PDI, make ready etc. and that will hurt the numbers on the first tank.