Fixed GUILabel with WorldToScreenPoint

Hi,

I'm trying to get a GUILabel to be fixed to a location using WorldToScreenPoint. So far it is ok only if I move in the x-axis, the label stays fixed. The moment I move in the y-axis the label goes bonkers and starts moving up and down with the camera!

 using UnityEngine;
 using System.Collections;
 
 public class Test : MonoBehaviour 
 {
     float speed = 0.5f;
     Vector3 ScreenPos;
 
     void Update () 
     {
         float hori = Input.GetAxis("Horizontal");
 
         if(hori > 0)
         {
             transform.Translate(Vector3.right * speed);
         }
         else if(hori < 0)
         {
             transform.Translate(-Vector3.right * speed);
         }
 
 
         float vert = Input.GetAxis("Vertical");
 
         if (vert > 0)
         {
             transform.Translate(Vector3.up * speed);
         }
         else if(vert < 0)
         {
             transform.Translate(-Vector3.up * speed);
         }
 
         ScreenPos = Camera.main.WorldToScreenPoint(new Vector3(0, 0, 0));
     }
 
     void OnGUI()
     {
         GUI.BeginGroup(new Rect(ScreenPos.x, ScreenPos.y, 200, 100));
             GUI.Label(new Rect(0, 0, 190, 50), "I DONT WANT TO MOVE");
         GUI.EndGroup();
     }
 }