Call for service now. You don't want to mess with leaking gas.
First thing, make sure your gas cap is on tight. And that you are not overfilling the car at the station or spilling gas. Assuming you have checked that,
The main causes of gas odor are flooding when starting, a leaking oil filler cap, broken or leaking spark plugs, or a leak in the gas tank/filler/fuel lines. That's the one you should be worried about. I had a car with a cracked gas filler, gas pooled on top of the tank and later caught on fire: the car was completely engulfed within 45 seconds and i was lucky to get out alive.