Problem with TTP229-BSF using Arduino Uno

Question

I'm trying to use a 16-channel capacitive touch sensor named TTP229-BSF with an Arduino Uno. I use the following code it works correctly when i touch directly but when i place two 4 mm plexiglass pads on top and try to touch over them some times wrong numbers are printed out in the serial terminal. I linked the required jumper as shown in the attached picture. i used 22p capacitors instead of the existing 33p sensitivity capacitors for increasing sensitivity

What is the problem here?

Is there a better and more robust way to do this based on the timing diagram of the datasheet that I attached?

#define SCL_PIN 8
#define SDO_PIN 9

/* Used to store the key state */
byte Key;

void setup()
{
  /* Initialise the serial interface */
  Serial.begin(9600);
  /* Configure the clock and data pins */
  pinMode(SCL_PIN, OUTPUT);  
  pinMode(SDO_PIN, INPUT); 
}


/* Main program */
void loop()
{
  /* Read the current state of the keypad */
  Key = Read_Keypad();
  
  /* If a key has been pressed output it to the serial port */
  if (Key)
  { 
  Serial.println(Key); 
  }
     

  /* Wait a little before reading again 
     so not to flood the serial port*/
  delay(300);
}


/* Read the state of the keypad */
byte Read_Keypad(void)
{
  byte Count;
  byte Key_State = 0;

  /* Pulse the clock pin 16 times (one for each key of the keypad) 
     and read the state of the data pin on each pulse */
  for(Count = 1; Count <= 16; Count++)
  {
    digitalWrite(SCL_PIN, LOW); 
    
    /* If the data pin is low (active low mode) then store the 
       current key number */
    if (!digitalRead(SDO_PIN))
      Key_State = Count; 
    
    digitalWrite(SCL_PIN, HIGH);
  }  
  
  return Key_State; 
}