Insert Interstitial between scenes and close the ad before changing the scenes in Unity,

I'm using AdMob interstitial ads, everything works fine. unfortunately the ad appears for about 1 second and disappears then scene is loaded. The user has no time to close the ad. What condition can I use if I want the scene to load only after the ad is closed?

 using System.Collections;
         using System.Collections.Generic;
         using UnityEngine;
         using UnityEngine.SceneManagement;
         using GoogleMobileAds.Api;
         using UnityEngine.UI;
         using System;
     
     public class AdManager : MonoBehaviour
     {
         public static AdManager Instance { get; set; }
     
         
         private InterstitialAd interstitial;
         
     
     
     void Start()
     {
         #if UNITY_ANDROID
             string appId = "";
         #elif UNITY_IPHONE
             string appId = "todo";
         #else
             string appId = "";
         #endif
         
         this.interstitial = new InterstitialAd(appId);
     }
     
     public void ShowInterstitial()
     {
         RequestInterstitial();
     
     } 
     
     
     
     public void RequestInterstitial()
     {
         #if UNITY_ANDROID
             string interstitialId = "ca-app-pub-3940256099942544/1033173712";
         #elif UNITY_IPHONE
             string interstitialId = "unexpected_platform";
         #else
             string interstitialId = "unexpected_platform";
         #endif
     
         if(interstitial !=null)
         interstitial.Destroy();
     
         interstitial = new InterstitialAd(interstitialId);
     
         interstitial.OnAdLoaded +=HandleOnAdLoaded;
     
         interstitial.LoadAd(CreateNewRequest());
     
     }
     public void HandleOnAdLoaded(object sender, EventArgs args)
     {
         if(interstitial.IsLoaded())
         interstitial.Show();
     }
         
     
     private AdRequest CreateNewRequest()
     {
         return new AdRequest.Builder().Build();
     
     }
     
     
     }

//Change scene code I am using:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.SceneManagement;
 
 public class ChangeScene : MonoBehaviour
 {
 
 public void LoadScene(string sceneName)
 {
     
     SceneManager.LoadScene(sceneName);
     
 }
 
 }