it is a small engine in a big vehicle- it's going to have to work a little harder to keep the thing moving.
plus, it is winter time, and you were going kind of fast.
wait until the summer gas blends are out and drive closer to 60 and then see how it does.
my brother has an '04 Cavalier with the 2.2 Ecotec engine in it, and the best he's ever gotten was 34mpg. he bought the car brand new.
my 2.2 (not Ecotec- the trusty old bulletproof pushrod motor that the Ecotec replaced) 97 Cavalier was up to 39.8mpg when i sold it last summer, with 33 being the worst fuel economy i ever got with that car.
but my brother's car is a lot faster and just more fun to drive than my car was- even tho mine was a 5 speed and his is an auto.