The relationship between pressure and volume is described by Boyle's Law, which states that at a constant temperature, the pressure and volume of a gas are inversely proportional. This means that as the volume increases, the pressure decreases, and as the volume decreases, the pressure increases.
However, it is important to note that the relationship between pressure and volume is not always perfect and there are many factors that can affect the measurements. For example, if the apparatus used to measure the pressure and volume is not calibrated properly, or if there is a leak in the system, this can lead to inaccurate results. Additionally, external factors such as temperature changes or the presence of impurities in the gas can also affect the measurements.
It is possible that the reason for your observation is an experimental error, or if not, it could be that you have discovered something new or an exception to the Boyle's Law. I recommend you to repeat the experiment and check your measurements and equipment, also double check your calculations and notes.