First Fill up, Wrong "Average fuel consumption" in Stats

what is the correct way for input the first fill up of a new car?

I have bought a new car. There was about 7 kilometers on the tacho and still some fuel in the tank (perhaps about 10 or 15 liters, don't know how much exactly) when i fill up the first time. I filled up until max, wrote the data into fuelio and checked the option "Missed previous". Now after 2nd and 3rd fill up, I recognized that the calculated data of "average fuel consumption" under Stats seems not calculated correctly, it's much to low.

Any suggestions what I can do to get the correct values?

Greetings

Basti