Yes your car needs tuning
my alto gives around 165-170km in the city, without AC.
But my Cylinder is factory fitted 55kg, and the pump fills up around 9.25KG of cng in it when its empty.
Please check how many Kg's of CNG are getting filled in your car.
If the tuning is right, then the car should give around 17-18km/Kg of CNG average.
Maybe the CNG pump has less pressure, try filling from another pump.
Hopefully it will solve your problem