Help loading fuel

[Bruce]

Top of the day to all. Can someone direct me how to do this right. I planned a flight and the flight plan say i would use 778gls of fuel since i was flying the 737-800 which has a center, left and right tanks i devided the 778 by 3 and add 16 more gls making it a total of 794gls but ran out even before a reach the desired altitude and around 10mins into the flight. Help me please how to do this right.

[Tai-2]

In game fueling thing is not the best.
Plus you have to consider the amount of throttle you had(if auto throttle, then the wind speeds) because I remember doing a Flight from MIA,to Osaka and I had heavy winds that made me have to land at another airport.