I don't know anything about the megane your driving but it sounds more like a leaking injector or fuel line than a potentiometer fault, though I agree it could cause the excessive revving.
It may be worth having a look at it if you're handy that way, hopefully someone else on the forum will step in with a way of checking out the Megane
and potentiometer for problems.
If you can smell petrol then it's potentially dangerous to drive or even start the car as you shouldn't smell petrol under any circumstances whilst driving.
Sorry to be alarmist but a fuel leak in the engine bay?
- As far as fuel leaks go that's a worst case scenario.
In all honesty, if the petrol smell is strong then it clearly indicates a leak of some kind. I'd personally call a mobile mechanic to come and look at the car and check the fuel lines and injectors for leaks before driving it again.
Please take care.
As a fellow parent this one worries me.