Banner ad multiplies after scene reload and shows up too late that affects the game performance

Here is the video to demonstrate the problem. As you see, the banner ad shows up and make the screen smaller, this, I understand. However, How do I make it appear before I start playing (finish loading the ad before playing or do I have any way to make a space just for ad?), because when it shows up, it makes the buttons move a bit and it’s annoying.
Second problem, Every time I reload the scene, the old ad is still there and it multiplies like in the video. How do I stop it? thank you guys for helping me.
Here is the code for ad in my game.