This code does not work

Hi!

I got this code. I use it for making the weapon sway but it doesn't do anything. I already had another one but this wasn't smooth enaugh, so I tried to implement iTween. Where's the matter in this script?

 #pragma strict
 
 public var MoveAmount : float = 1;
 public var MoveSpeed : float = 2;
 public var GUN: GameObject;
 public var MoveOnX : float;
 public var MoveOnY : float;
 public var DefaultPos : Vector3;
 public var NewGunPos : Vector3;
 private var go :GameObject;
 function Start(){
     DefaultPos = transform.localPosition;
     go = new GameObject("Weapon Bobbing");
 }
 
 function Update(){
     MoveOnX = Input.GetAxis("Mouse X") * Time.deltaTime * MoveAmount;
     MoveOnY = Input.GetAxis("Mouse Y") * Time.deltaTime * MoveAmount;
     
     iTween.MoveTo(go, iTween.Hash("x",DefaultPos.x + MoveOnX, "y", DefaultPos.y + MoveOnY, "time", MoveSpeed));
     
     GUN.transform.localPosition.x = go.transform.position.x;
     GUN.transform.localPosition.y = go.transform.position.y;
 }