bhai you can check yourself if there is a leak in your car all you have to do is following
a)you have to check the Cng level giving in the engine compartment area when your done with your driving park the car and note down the gas pressure leave the car for couple of hours check again if the level drops means you have a leak in the car which can be dangerous i'll suggest if there is a leak go to a professional and get it fixed!
B) please check your exhaust system for leaks as it also gives smel of gas when the engine is runiing
one more thing do you smell this when you go to gas filling station while filling or when you are driving your car??