How much does this error cost in kilograms?

For a while, we have been working on the WT3 configuration of our UAV, that is, the wing-tail rocket engine configuration. For the design and analysis of our project, I use Matlab. Yesterday, while updating the input data on systems and avionics, I discovered two errors in my calculations. The first error was related to the estimation of battery mass, where I used Wh/kg rather than J/kg as the units of specific energy. The conversion factor is 3600! In my early versions of the code, I set too low values of the required energy for the onboard equipment, so it was difficult to detect this error. I had to correct the input data on systems and equipment first! Another error was related to my spline interpolation model for the prediction of the rocket engine mass. It turned out that my spline model yielded an engine mass three times higher than it had to be! What was the cost of these errors? Around 70 kg of airplane gross mass, 20 m2 of wing area, and 2 m of average wing chord, which rendered the WT3 configuration unfeasible. With an aspect ratio of 2, the wing root chord was larger than the aeroshell diameter, see the figure.