the meter is not accurate. you will need to keep driving the car. this average will increase gradually.
you can also reset this meter. do this when driving at a constant speed on open road. long press the meter button, to reset it to zero. it will start fresh reading.
average will increase or decrease based on your driving style / conditions.
more accurate measurement, is fill up the tank fully to the top of the filler neck.
drive around as you normally do.
after 300 kms, fill up your tank again to the top of filler neck. preferably use the exact same pump as well from where you filled earlier. note down how many liters go into the tank.
divide the 300 km by the number of liters to get a more accurate fuel average.