Why the gui texture is not in the middle of the screen and how can i change the texture size ?

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class CrossHair : MonoBehaviour
 {
     public Texture2D crosshairTexture;
     public Rect position;
     public bool originalOn = false;
 
     private void Start()
     {
         Cursor.lockState = CursorLockMode.Locked;
 
         position = new Rect((Screen.width - crosshairTexture.width) / 2, (Screen.height -
          crosshairTexture.height) / 2, crosshairTexture.width, crosshairTexture.height);
     }
 
     private void OnGUI()
     {
         if (originalOn == true)
         {
             GUI.DrawTexture(position, crosshairTexture);
         }
     }
 }
 

The texture is too much to the left side not in the middle. And it's very big i want it to be very small almost like a dot(cross hair).