So it smells like gas, when you first turn it on, or it smells like gas all the time when it is on ?
Either way, i would say that some part of the fuel system is leaking and gasoline vapors are being drawn into the hood cowl vents, when the heater vents are drawing in fresh outside air.
I would consider this a serious condition that warrants immediate attention.
Get it to the shop quick before calamity strikes.
At this point, until a complete inspection is done, it would be impossible to say where the problem area is, although you did say that all you have done is change the oil for the last 120k, so it may be something that has been overlooked.
Besides the fact that breathing gasoline vapors is not good, your car may catch on fire.