Invoke is not working properly.

Hello, I am trying to create a bullet spawn using the invoke function but it is not working. Instead of creating a bullet every 3 seconds, it is waiting 3 seconds and then contionusly creating bullets non stop. Am I not using this function properly.

Also, I am using the MobileSingleStickControl in the unity package as my shooting joystick. I have attached a trigger event on the joystick which is calling the "shoottrig" function below. It is using the PointerDown to set it to true, and PointerUp to set it to false.

Here is the code, please help. Thanks.

 var shooting : boolean;
 var projectile : Rigidbody; 
 var speed = 20;
 
 function Update () { 
 
 //Face Joystick Direction
     var joystickHorizontal = UnityStandardAssets.CrossPlatformInput.CrossPlatformInputManager.GetAxis("Horizontal"); 
     var joystickVertical = UnityStandardAssets.CrossPlatformInput.CrossPlatformInputManager.GetAxis("Vertical"); 
     transform.LookAt(transform.position + Vector3(joystickHorizontal, 0, joystickVertical), -Vector3.forward);
      
 //Shooting triggered     
     if(shooting){
                Invoke("Shooting", 3.0f);
       }
  }
 //Creating shooting functions
 
 function Shooting(){
 Debug.Log("we are shooting");
 
 
 //TESTTTT
 var clone : Rigidbody;
  clone = Instantiate(projectile, transform.position, transform.rotation);
  // Give the cloned object an initial velocity along the current
  // object's Z axis
  clone.velocity = transform.TransformDirection (Vector3.forward * speed);
  
 
 }
 //Function called through the PointerDown trigger. 
 function shoottrig(which : boolean){
         shooting = which;
  }