Hi Patrick,

It's very likely that's caused by the fuel tank vent system and shouldn't be anything to worry about. 

However, it is worth checking for fuel leaks. Make sure the garage floor is completely clean and dry and then leave the car running for a few minutes, checking underneath for leaks. Do the same without the car running, but leave it for longer.

If you find no leaks, but you're still not comfortable with the smell, bring the car along to a good mechanic.