Dealing with fear of what could go wrong?

I adopted my first dog two weeks ago and to say he’s been a great dog is really an understatement. He’s extremely well mannered and while he needs some reinforcement on good skills it’s evident he was pretty well trained before ending up in a shelter. For context he’s a large dog but I fell in love with him when I met him. Now that I have him and am getting him adjusted to my life there’s always the nagging feeling in my mind of what and when is something going to go wrong. Is he going to tear up the house while I’m gone? Is he going to lunge at a child on a walk? Bark his head off? Snap at ME? He’s shown very few tendencies for any of this but I’m having a hard time settling into accepting that. For those who may have felt similar, how long before you really felt confident in your dog and his training?