Have you ever wondered what the N is for on the gearshifter?  It’s not useful for parking. It’s not needed to push the car when the engine is off (you can do that in any gear).  It’s the safety gear. If anything were to happen that prevented you from slowing the engine down by letting off the gas pedal, just shift to neutral. The engine might not like spinning so fast but the brakes and power steering will still work normally. If you turn off the engine, the brakes and steering will still work, but will require significantly more effort to use, as these systems are powered by the engine.

So, if the engine won’t slow down, just shift to neutral.