Flick ball in 3D

Hi, I am trying to create a mobile game where the user can shoot a ball at a target, by flicking the screen, in 3D.

So far I have managed to move the ball based on the users "flick" including the power of the flick, However the ball only moves up/down and sideways. I want the ball to move more "forward" than up.

In the picture included, the top diagram illustrates the current behaviour, and the bottom diagram illustrates what the movement I am trying to achieve:

the green arrows in the diagram are the users input and the red arrows are the ball movement.

I have had to swap between the y and z axis because of other aspects of the game

This is the code I am using (from: ): using UnityEngine; using System.Collections;

 public class TouchMonitor : MonoBehaviour {
  
     public Rigidbody ball;
  
     private Vector3 touchStart; 
     private Vector3 touchEnd;
     private GameObject lineRenderer;    
  
     void Update () {
         if (Input.touchCount > 0)
         {
             Touch t = Input.touches[0];
             if (t.phase == TouchPhase.Began)
             {
                 touchStart = t.position;
             }
  
             if (t.phase == TouchPhase.Ended || t.phase == TouchPhase.Canceled)
             {
                 touchEnd = t.position;
                 DoInput();
             }
         }
  
         if (Input.GetButtonDown("Fire1"))
         {
             touchStart = Input.mousePosition;
         }
  
         if (Input.GetButtonUp("Fire1"))
         {
             touchEnd = Input.mousePosition;
             DoInput();
         }
     }
  
     void DoInput()
     {
         Vector3 p1 = new Vector3();
         Vector3 p2 = new Vector3();
         touchStart.z = Camera.main.nearClipPlane+.1f; //push it a little passed the clip plane for camera, just to make sure its visible on screen
         touchEnd.z = Camera.main.nearClipPlane+.1f;
         p1 = Camera.main.ScreenToWorldPoint(touchStart);
         p2 = Camera.main.ScreenToWorldPoint(touchEnd);
  
         CreateLine(p1,p2);
  
         Vector3 v = p2-p1;
         //v.Normalize();
         ball.AddForce(v*500, ForceMode.Impulse);
     }
  
     //creates an ugly purple line from pos1 to pos2 in worldspace
     void CreateLine(Vector3 p1, Vector3 p2)
     {
         Destroy(lineRenderer);
         lineRenderer = new GameObject();
         lineRenderer.name = "LineRenderer";
         LineRenderer lr = (LineRenderer)lineRenderer.AddComponent(typeof(LineRenderer));
         lr.SetVertexCount(2);
         lr.SetWidth(0.001f, 0.001f);
         lr.SetPosition(0, p1);
         lr.SetPosition(1, p2);
     }
 }

and to swap between the axis:

 using UnityEngine;
 using System.Collections;
 
 public class Gravity : MonoBehaviour {
 
     private Vector3 gravity; 
  
     // Use this for initialization
     void Start () {
           gravity = Physics.gravity;
     }
  
     // Update is called once per frame
     void Update () {
  
             gravity.x = 0;
             gravity.y = 0;
             gravity.z = -20;
             Debug.Log("Gravity Z");
       
         Physics.gravity = gravity;
     }
 }

This is my first attempt at creating a game and I am learning as I go along. Any suggestions would be greatly appreciated!