Fuel is burned throughout the flight, not just take-off (and initial climb to altitude), which is why airliners flying long-haul routes usually gain altitude as they progress. The Cessna 172 seems to have a fuel fraction of around 20% (an order of magnitude higher than a car), and airliners are much higher (~40%).[1][2]

[1] https://en.wikipedia.org/wiki/Cessna_172

[2] https://en.wikipedia.org/wiki/Fuel_fraction