Getting mileage as low as 20L/100KM, What could be the reason?

[Nahid]

I bought a 2010 Vitz (new shape) last month. It's 1300 cc. It's a reconditioned car, that is it was used in Japan for about 5 years before it came to my country (Bangladesh). When I bought it the seller has changed all the lubricants. I found it at 36000 KM mileage and I drove about 200 km so far. I drive my car on octane.

Now the thing is I'm getting very low mileage. It's about 5-6 KM per liter (in other word, 18-20L/100 KM). I know it's ridiculously low mileage. Although we have heavy traffic here, so at least 10 KM per liter or 10L/100KM is expected according to other guys who drive in my city.

It's my first car and I'm not very expert about car mechanism. Could anyone please tell me what could be the reason of this?