Bad mileage 12km/l only

I had purchased this car Eon Magna plus in 2014 . I drive this approx 45000 km everything is good for this car but mileage is little bit lower then other compitators like alto k10 . It gave me same mileage in city and highway for both i get 12 km/l . I drove on 60-70 kmp/h ,When ever i drive this car for little distance approx 100 km then i had to pay 700 Rs for petrol (Rs700/83 petrol price in punjab =8L x12km/l =101km ) Car exterior Look is also little bit small nobudy gave u side for overtaking.