Have an object move towards the mouse, but...

Hey guys, I have this code for a bullet that heads to the mouse's position when created. It works and all, but I have one problem. When the bullet reaches the point where the mouse was clicked, it stops there. How can i get the bullet to keep going past there?

Here's my code

 sing UnityEngine;
 using System.Collections;
 
 public class BulletRight: MonoBehaviour {
     
     public int timer = 100;
     public float speed = 40f;
     public float RotationSpeed=100;
     public float distance;
     
     //values for internal use
     private Quaternion _lookRotation;
     private Vector3 _direction;
     private Vector3 targetPos;
     
     // Use this for initialization
     void Start () {
         distance = transform.position.z - Camera.main.transform.position.z;
          targetPos = new Vector3(Input.mousePosition.x, Input.mousePosition.y, distance);
          targetPos = Camera.main.ScreenToWorldPoint(targetPos);
     }
     
     // Update is called once per frame
     void Update () {
         timer--;
         
         transform.position = Vector3.MoveTowards (transform.position, targetPos, speed * Time.deltaTime);
         
         if(timer<0)
             Destroy(gameObject);
     }
 }

any help would be appreciated!