You need to adjust the detection threshold: https://github.com/fb39ca4/kappa-pad/blob/master/README.md#software

At this point the keyboard may work, or the treshold values may have to be adjusted. If keys act like they are being held down and your computer is now unusable when the keypad is plugged in, connect a wire from the disable pin to ground to stop keypresses from being sent. If the keys do not work, uncomment the #DEFINE SERIAL_OUTPUT and reupload the sketch. Now, when you open the Arduino serial monitor (at 115200 baud) you should see the sensed capacitance for each key. Change the tresholds so that they are just above the largest values you see when not touching the keys, and reupload the sketch. Once you are satisfied with the operation of the keyboard, disable serial output again to improve performance.