really need help with 4 servos with the arduino

this code runs 3 of the servos like a champ but when i add in the 4th one i got all the same problems, so i chained the code to work the other servo and not the first one i tryed and those 3 ran like a champ. man 1, 2, 3 servos ok, but 4 no way

#include <MegaServo.h>



MegaServo servo1;
MegaServo servo2;
\\ see i cut servo3 
MegaServo servo4; // the frist time i cut servo 4 and left in 3
int potpin1 = 0;  // analog pin used to connect the potentiometer
int potpin2 = 1;

int potpin4 = 3;
int val;    // variable to read the value from the analog pin

void setup()
{
  servo1.attach(9);  // attaches the servo on pin 9 to the servo object
  servo2.attach(10);  // attaches the servo on pin 10 to the servo object
  
  servo4.attach(11);
}

void loop()
{
  val = analogRead(potpin1);            // reads the value of the potentiometer (value between 0 and 1023)
  val = map(val, 0, 1023, 0, 179);     // scale it to use it with the servo (value between 0 and 180)
  servo1.write(val);                  // sets the servo position according to the scaled value
  val = analogRead(potpin2);            // reads the value of the potentiometer (value between 0 and 1023)
  val = map(val, 0, 1023, 179, 0);     // scale it to use it with the servo (value between 0 and 180)
  servo2.write(val);      
      
  val = analogRead(potpin4);            // reads the value of the potentiometer (value between 0 and 1023)
  val = map(val, 0, 1023, 0, 179);     // scale it to use it with the servo (value between 0 and 180)
  servo4.write(val);                        // sets the servo position according to the scaled value
  delay(15);                           // waits for the servo to get there
}