cal≠kcal

1 gallon gasoline contains 31 million small calories, while the human caloric requirements are given in large calories. 1000 small calories = 1 large calorie. So the calculations are off by a factor of 1000. The confusion stems from the fact that both are commonly referred to as “calories”, for some stupid reason.

So in reality you would have to drink another gallon in just 2-3 weeks.