Object reference not set to an instance of an object in c#.

Hi guys! I have some problems with script. I want my game to start after i press on the screen, if i dont press on the screen i want my game not to start. I hope you understand what i mean.

this is my script

 using UnityEngine;
 using System.Collections;
 
 public class StartScreen1 : MonoBehaviour {
 
     public bool sawOnce = false;
     
     void Start () {
         if (!sawOnce) {
             GetComponent<SpriteRenderer>().enabled = true;
             Time.timeScale = 0;
         }
         sawOnce = true;
     }
     
     void Update () {
         
         if (Time.timeScale == 0 && (Input.GetMouseButtonDown (0))) {
             Time.timeScale = 1;
             GetComponent<SpriteRenderer>().enabled = false;
             Destroy(this.gameObject);
         }
     }
 }

but this script don't working. My game starts without press. Help please