When the gas pump nozzle clicks off automatically, DO NOT add a little more gas. You need extra room in your gas tank to allow the gasoline to expand. Topping off your gas tank is bad for the environment and your wallet. Any additional gas you try to pump into your tank may be drawn into the vapor line and fed back into the station’s storage tanks. (Of course you're still paying for this extra gas).
If you top off your tank, the extra gas may evaporate into your vehicle’s vapor collection system. That system may become fouled and will not work properly causing your vehicle to run poorly and have high gas emissions. Also the passenger compartment may have a gasoline odor and in worst cases, the car to catch fire.
The gas nozzle automatically clicks off when your gas tank is full. Did you read that last sentence?
The gas nozzle automatically clicks off when your gas tank is full. It's full. Don't try to put more gas in the tank.