Vuforia AR: Access only two axis in transform,position

I am creating an Android AR app where a UI element is following a 3D object. It works fine and my only problem is I want to make the position ignore the Y axis in the target objects position so it wont move forward and backward.

This is the code that I got from searching on Youtube tutorials

public class WorldSpaceButton : MonoBehaviour { [SerializeField] private Transform targetTransform; private RectTransform rectTransform;

 private void Awake()
 {
         rectTransform = GetComponent<RectTransform>();
 }


 void Update()
 {

     var screenPoint = Camera.main.WorldToScreenPoint(targetTransform.position);
     rectTransform.position = screenPoint;

 }

And here is where the slider is going forward/backward when moving the camera close/far to the image target.

Hope someone can help me in this problem. I'm stuck because I don't know what to do next. Thanks!