I agree with kendal. Get him into a class NOW. Wrigley can learn to be ok around dogs. As started it can be more work, but it should be fixable at his age. If you keep waiting though, it will get worst, fast.
Be sure to not feed him the day of class but a small snack in the early morning. This way he won't just be hiding and scared, but hungry too, hopefully enough to get him over it and focused on you. This way he can start forgetting his fear.
Get a treat bag, and get some really good treats. My dogs favs are string cheese, hot dogs, and real cooked chicken. You have to wow him so much he can focus through the stress (at first, then he'll love it) so try a few things before class and find something he'd die for.
And even though it's hard, do. not. stress. Dogs are fabulous at reading us. If you are hovering, baby talking, picking him up, ect. Then he will assume class is bad, after all, look how worried you are? He'll start to get so much better with classes, be confident of the fact and don't make a big deal of any fear he shows. Try to get into a real class if possible, petsmart, petco ect don't really have good trainers, they just teach the basics and that's it most times.