I want the pitcher to throw a ball to a target a location inside a GUI panel

I am wanting the user to mouse click a location inside the GUI Panel and have the pitcher throw the ball to that location in the panel.

The problem that I am having is even though I click a point in the panel the balls trajectory is way off. Could it be that when I convert from screen space to world space the target point in world space is wrong ?

Here is the code:

 using UnityEngine;
 using System.Collections;
 
 public class PlayerPitcher : MonoBehaviour 
 {
     public GameObject ball;
     public GameObject parentBoneToBall;
     public float ballForceX = 0.07f;
     public float ballForceY = 0.5f;
     public float ballForceZ = -3.0f;
     private Animator animator;
     private bool InMyState = false;
     private GameObject ballClone;
     private bool startPitchAgain = true;
     Vector3  targetDirection  =  Vector3.zero;
     Vector3 pitchTarget = Vector3.zero;
 
 
 
     // Use this for initialization
     void Start () 
     {
         animator = GetComponent<Animator>();
         //ball.transform.parent = parentBoneToBall.transform;
         ballClone = Instantiate(ball, ball.transform.position, ball.transform.rotation) as GameObject;
         ballClone.transform.parent = parentBoneToBall.transform;
         ballClone.rigidbody.useGravity = false;
     }
 
     private void UserThrowingPitch()
     {
         if (Input.GetMouseButtonDown (1) && startPitchAgain) 
         {
 
             animator.SetBool ("isThrowingFastBall", true);
     
 
             float distance = 10.0f;
             pitchTarget = Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y, 100));
             Debug.Log("Mouse Target in World Space" + pitchTarget);  
 
             startPitchAgain = false;
         }
         
         if(this.animator.GetCurrentAnimatorStateInfo(0).IsName("Pitcher Base Layer.Pitch_ThrowFastBall"))
         {
             // Avoid any reload.
             InMyState = true;
         }
         else if (this.InMyState)
         {
             InMyState = false;
             // You have just left your state!
             animator.SetBool ("isThrowingFastBall", false);
             ballClone = Instantiate(ball, parentBoneToBall.transform.position, parentBoneToBall.transform.rotation) as GameObject;
             ballClone.transform.parent = parentBoneToBall.transform;
             ballClone.rigidbody.useGravity = false;
 
             startPitchAgain = true;
         }
     }
 
     // Update is called once per frame
     void Update () 
     {
         UserThrowingPitch ();
     }
 
     private Vector3 calculateBestThrowSpeed(Vector3 origin, Vector3 target, float timeToTarget) {
         // calculate vectors
         Vector3 toTarget = target - origin;
         Vector3 toTargetXZ = toTarget;
         toTargetXZ.y = 0;
         
         // calculate xz and y
         float y = toTarget.y;
         float xz = toTargetXZ.magnitude;
         
         // calculate starting speeds for xz and y. Physics forumulase deltaX = v0 * t + 1/2 * a * t * t
         // where a is "-gravity" but only on the y plane, and a is 0 in xz plane.
         // so xz = v0xz * t => v0xz = xz / t
         // and y = v0y * t - 1/2 * gravity * t * t => v0y * t = y + 1/2 * gravity * t * t => v0y = y / t + 1/2 * gravity * t
         float t = timeToTarget;
         float v0y = y / t + 0.5f * Physics.gravity.magnitude * t;
         float v0xz = xz / t;
         
         // create result vector for calculated starting speeds
         Vector3 result = toTargetXZ.normalized;        // get direction of xz but with magnitude 1
         result *= v0xz;                                // set magnitude of xz to v0xz (starting speed in xz plane)
         result.y = v0y;                                // set y to v0y (starting speed of y plane)
         
         return result;
     }
 
 
     public void ReleasePitch(AnimationEvent animEvent)
     {
         Debug.Log("PitchReleased");
     
         targetDirection = pitchTarget - parentBoneToBall.transform.position;
         ballClone.transform.LookAt(pitchTarget);    
         ballClone.transform.parent = null;
         ballClone.rigidbody.useGravity = false;
 
         Debug.Log("PitchTarget" + pitchTarget); 
 
         pitchTarget.z *= -1.0f;
 
 
         Vector3 throwSpeed = calculateBestThrowSpeed(parentBoneToBall.transform.position, pitchTarget, 0.3f);
         ballClone.rigidbody.AddForce(throwSpeed);
 
     }
 
     public void DestroyBall()
     {
         Destroy (ballClone);
     }
 }