Look for fuel leaks in the engine bay or back by the tank where you fill up the the tank. A little bit of gas will go a long way so if you had spilled a little while removing the nozel at the gas station the filler neck will disperse of it, sometimes it gathers on the inside of the fender, and causing for a smell that may not be an issue. On the other hand if you notice the smell under the hood you may have a leaking fuel line, check to see if anyone has replaced the fuel filter recently sometimes the technician does not tighten the lines securely causing a little fuel leak. other times its just a little fuel spray from not releasing the pressure before removing the filter may have sprayed the fuel on the car onto maybe the insulation. One thing to do is look under the car while it is running myabe after filling it up to check for leaks. If your notice a drip while the A/C is running dont be alarmed as this is the condensation dripping off as it is supposed to.