Hm, does that change anything? Atoms per molecule doesn’t seem important when we’re talking about the total weight. If anything jet fuel isn’t pure carbon so the math works out to create less CO2 than I calculated?

I don't think the number of atoms directly matters. However, the amount of energy that is released when kerosene burns has a _small_ impact. Because that energy was contributing to the mass of the kerosene (E=mc^2). But, that difference in mass will be tiny. Far surpassed by the mass of the non-carbon atoms in kerosene.