Blowing the lid off the tin

In this experiment, you fill the tin with gas from the bottom,  ignite the gas and pull out the tube from the bottom. The gas burns with a yellow flame through the hole in the lid for a while. Convection pulls in air through the hole in the bottom. The reaction must head more towards complete combustion because the flame ceases to be orange. Eventually the temperature inside gets so high that the pressure of air particles hitting the lid is too big. The lid almost hits the ceiling. I tried to do some calculations to find the temperature of the gas inside the tin when it explodes.

The tin felt warm to the touch after the experiment so I estimated a temperature rise of 20 degrees Celsius. The method leads to a suggest that the temperature of the gas rose by over 20000 degrees Celsius. This is clearly not true so there must be a flaw in the logic somewhere. I have assumed that all of the energy released by combustion goes to heat the tin and the gas inside it but the flame is burning outside so this assumption is flawed.