This goes against the thought that PV is constant. It turns out that T was not kept constant. This makes sense because as the more pressure, the less volume in the syringe. With less room in the syringe, more collisions among the atoms in the gas. More collisions means more energy.
More energy means a higher temperature.
So therefore, temperature was not constant. As usual, I must give a brief overview of the problems that stood in our way of experimental perfection. For one thing, we went into this experiment with the wrong frame of mind. We had no idea that temperature was not constant. We assume that it was constant for every trial.