Admob code question

I just finished my first game and I'm trying to practice how to put admobs in it. I just want to make sure that I don't call it multiple times with my code because I read that I might get in trouble for that.

Here's my code:

 void Start () {
     admob = GetComponent<AdMobPlugin>();
     admob.CreateBanner(AD_UNIT_ID, AdMobPlugin.AdSize.SMART_BANNER, false, "", false);
     admob.RequestAd();
     admob.ShowBanner();

 }
 
 // Update is called once per frame
 void Update () {

     if (Application.loadedLevelName == "Stage")
     {
         if (!hidden)
         {
             admob.HideBanner();
             hidden = true;
         }
     }
     else if (Application.loadedLevelName != "Stage")
     {
         if (hidden)
         {
             admob.ShowBanner();
             hidden = false;
         }
     }
 }