Ball Isn't following Trajectory line : Unity3d

Hello Everyone,

I am working on projectile motion. Sometimes my ball does not follow the trajectory line.

Code is here :

 #pragma strict
 #pragma implicit
 #pragma downcast 
 var turret : Transform; 
 var bulletPrefab : Transform;
 private var plane : Plane;
 private var power : float = 30;
 private var gravity: float = 9.8;
 public var distance : float = 1.0f;
 public var  predictionLine : LineRenderer;
 public var enablePrediction : boolean = true;
 public var targetPoint : boolean = true;
 var velocity : Vector3;
 
 
 private var horizontalOffset : float = 0.0f;
 private var  lob : float = 0.75f;
 var bullet : Transform ;
     
 function Awake ()
 {
     plane = Plane(-Vector3.forward,turret.position);
     predictionLine.SetWidth(1.0f,1.0f);
     bullet = Instantiate(bulletPrefab, turret.position, turret.rotation);
 }    
 function Update () 
 { 
     var distanceToPlane : float;
     var hit : RaycastHit; 
     var ray = camera.ScreenPointToRay(Input.mousePosition);   
     var hitPoint : Vector3;
     
     if(plane.Raycast(ray,distanceToPlane))
     {
             hitPoint = ray.GetPoint(distanceToPlane);
             velocity = GetTrajectoryVelocity(turret.position, hitPoint, lob, Physics.gravity);    
             turret.up = velocity;
     }
     
 //    if(Input.GetMouseButtonDown(0))
 //    {
 //        if(plane.Raycast(ray,distanceToPlane))
 //        {
 //            GameObject.Find("SoccerBall(Clone)").transform.position = turret.position;
 //            FireProjectile();
 //        }
 //    } 
     
 
     horizontalOffset = Mathf.Clamp(horizontalOffset, -45.0f, 35.0f);
         
     lob += Input.GetAxis("Mouse ScrollWheel") * 0.01f;
     //Debug.Log("lob" + lob);
     lob = Mathf.Clamp(lob, 0.25f, 1.2f);
     
     distance = Mathf.Clamp(distance, 0.25f, 1.5f);
 
     UpdatePredictionLine();  
         
     if (Input.touchCount > 0) {
         var touch = Input.GetTouch(0);
         
         switch (touch.phase) {
         
         case TouchPhase.Began:
             UpdatePredictionLine();  
             break;
         
         case TouchPhase.Moved:
             UpdatePredictionLine();  
             break;
             
         case TouchPhase.Ended:
             GameObject.Find("SoccerBall(Clone)").transform.position = turret.position;
             UpdatePredictionLine();  
             FireProjectile();
             break;
            }
         }
     }
 
     
         function UpdatePredictionLine() 
         {
             predictionLine.SetVertexCount(180);
             var previousPosition : Vector3 = turret.position;
             for(var i : int = 0; i < 180; i++)
             {
                 var currentPosition : Vector3 = GetTrajectoryPoint(turret.position, velocity, i, 1, Physics.gravity);
                 var direction : Vector3= currentPosition - previousPosition;
                 direction.Normalize();
                 
                 var distance : float = Vector3.Distance(currentPosition, previousPosition);
                 
                 var hitInfo : RaycastHit ;
                 if(Physics.Raycast(previousPosition, direction,  hitInfo, distance))
                 {
                     predictionLine.SetPosition(i,hitInfo.point);
                     predictionLine.SetVertexCount(i);
                     break;
                 }
                 
                 previousPosition = currentPosition;
                 predictionLine.SetPosition(i,currentPosition);
             }
         }
         
         function GetTrajectoryPoint( startingPosition : Vector3 ,  initialVelocity : Vector3 ,  timestep : float,  lob : float ,  gravity : Vector3) : Vector3
         {
             var physicsTimestep : float = Time.fixedDeltaTime;
             var stepVelocity : Vector3 = initialVelocity * physicsTimestep;
             
             //Gravity is already in meters per second, so we need meters per second per second
             var stepGravity : Vector3 = gravity * physicsTimestep * physicsTimestep;
             
             return startingPosition + (timestep * stepVelocity) + ((( timestep * timestep + timestep) * stepGravity ) / 2.0f);
         }
         
         function GetTrajectoryVelocity( startingPosition : Vector3,  targetPosition : Vector3,  lob : float ,  gravity : Vector3) : Vector3
         {
             var physicsTimestep : float = Time.fixedDeltaTime;
             var timestepsPerSecond : float = Mathf.Ceil(1f/physicsTimestep);
             
             //By default we set n so our projectile will reach our target point in 1 second
             var n : float = lob * timestepsPerSecond;
             
             var a : Vector3 = physicsTimestep * physicsTimestep * gravity;
             var p : Vector3 = targetPosition;
             var s : Vector3 = startingPosition;
             
             var velocity : Vector3 = (s + (((n * n + n) * a) / 2f) - p) * -1 / n;
             //This will give us velocity per timestep. The physics engine expects velocity in terms of meters per second
             velocity /= physicsTimestep;
             return velocity;
         }
         
         function FireProjectile() {
             var rb : Rigidbody = GameObject.Find("SoccerBall(Clone)").GetComponent(Rigidbody);
             rb.useGravity = true;
             rb.transform.position = turret.position;
             
             rb.AddForce(velocity, ForceMode.Impulse);
         } 

So what can be the reason? While touching it is changing the velocity?? I could not identify the bug.

It is specially happening with large angle.

Thanks in advance for your help and support....