A simple 2D pong game doesn't run

So Hi, fairly new to the Unity.I was watching a tutorial on how to make a small 2D game called Pong, its really simple.I created the objects and even wrote the C# program properly. the program is basically just to move my paddle up and down using UnityEngine; using System.Collections;

public class paddle : MonoBehaviour {

 public float paddlespeed = 1;
 public Vector3 playerPos;

     void Update ()
 {
     float yPos = gameObject.transform.position.y + (Input.GetAxis ("Vertical") * paddlespeed);
     playerPos = new Vector3 (-20, Mathf.Clamp(yPos,-11,11),0);
     gameObject.transform.position = playerPos;
 }

} but when I run the game,it doesn't do anything.What am I missing ?