Help, can't get Grid to instantiate in the center of the screen

I have a Grid I'm instantiating at (0, 0, 0), but the Grid seems to be appearing in the top right of the screen

The Grid script is attached to an Empty Game Object positioned at (0, 0, 0) and the camera is also positioned at (0, 0, 0)

I don't understand what's happening here

my script

 using UnityEngine;
 using System.Collections;
 
 
 public class gridTest : MonoBehaviour 
 {
     
     public int GridWidth;
     public int GridHeight;
     public GameObject myPrefab;
 
     // Update is called once per frame
     void Start () 
     {
         //Create Empty GameObject
         GameObject newEmptyGameObject = new GameObject("Grid");
         
         for(int y=GridHeight; y>=1; y--)
         {
             for(int x=GridWidth; x>=1; x--)
             {
                 GameObject clone = Instantiate(myPrefab,new Vector3(x+x, y+y, 1),Quaternion.identity)as GameObject;
                 //Make clones Children of Grid
                 clone.transform.parent = newEmptyGameObject.transform;
             }
         }
     }
 }