GUI box not moving with game object on X axis

Hey,

I am trying to create a health bar above a spaceship in a 2d spaceshooter. Right now I just need to create a box and move it with the player. I found WorldToScreenPoint() which should work althought the box moves only on the Y axis, why is that?

This code is in Player.js attached to the ship gameobject

 // Gui render
 function OnGUI () {
 
     var PlayerPosition : Vector2 = Camera.main.WorldToScreenPoint(transform.position);
 
     print(PlayerPosition.x);
 
     GUI.Box(new Rect(PlayerPosition.x, PlayerPosition.y, 200, 200), 'Test');
 
 }

The print shows the changed position but the box only moves up and down.

Thanks!