I have purchased a new Chevy SPark

hi,
I have purchased a new Chevy SPark a month back. I have driven it around 2000Kms and had my first service too. ride quality is goo, its spacious. But every body is speaking about its wonderful fuel economy. But let me tell u, iam getting an average of just over 9 KMS in city with a/c switched. I dont know wat is the problem. Is there any serious problem with my vehicle? Do u people add any affluent with petrol? Please help me out. I really think that I should have purchased a Wagon-R LPG verion which would have given me a better mileage.