THIS IS NOT A PROBLEM, YOU DO NOT NEED TO GO TO A DEALERSHIP
The mileage meter works with the accelerator, the more you press it the less average you get.
Try it for yourself......
For example, when driving down the road at 40km/hr shift gear and dont press the accelerator, your avg will go to 99.9 km/l,,,,,,,,,
Similarly, floor ur accelerator and ur avg will be something like 6 km/l,,,,,,
Basically that meter gives you per/sec average or u may say average at the current time/type of driving...... Hope this clarifies.