Projectile Shooting Problem

I am using unity to create a penalty shoot-out game. I also have a power bar in the scene. Now when I click to shoot the ball, the first time , two balls are going off simultaneously . I would like only one ball to be shot . Thanks , and here is my script;

#pragma strict

// maximum width of the powerbar 
var fullWidth : float = 256;
 
//create a boolean flag we can use to stop and start the choosing of power
var choosing : boolean = false;
 
//create a private variable (not shown in inspector) to store the current set power
private var thePower : float;
 
//create a slot to assign my ball prefab to.
var ball : Rigidbody;
 
//create a slot to assign an empty game object as the point to spawn from
var spawnPos : Transform;
var staffingSpeed ;
 
// create a number to multiply the force by as the value of up to 256 may not be enough to
// effectively shoot a ball forward
var shotForce : float = 5;
 
function Update () {
 
 
 // detect if key is released and then call the Shoot function, passing the current
 // value of 'thePower' variable into it's 'power' argument
 if(Input.GetButtonUp("Jump")){
  Shoot(thePower);
 }
 
 if(!choosing){
  //create a power variable and set it to ping pong function
  //from current time to 1, and multiply that by a number (or variable holding a number)
  thePower = Mathf.PingPong(Time.time, 1) * fullWidth;
 
  //set the width of the GUI Texture equal to that power value
  guiTexture.pixelInset.width = thePower;
 }
}
 
// start the 'Shoot' custom function, establish a
// float variable to be fed with a number when function is called
function Shoot(power : float){
 
 
 //create a ball, assign the newly created ball to a var called pFab
 var pFab : Rigidbody = Instantiate(ball, spawnPos.position, spawnPos.rotation);
 
 //find the forward direction of the object assigned to the spawnPos variable
 var fwd : Vector3 = spawnPos.forward;
 pFab.AddForce(fwd * power*shotForce);
 
 //pause before resuming the power bar motion
 yield WaitForSeconds(2);
 
 
}

Check and make sure you do not already have a ball, in the scene before you run the game.