Well, I bet you won't do something like that again right? The thing I think you should do is put yourself in your kids shoes.
1. he is super excited to go to
Disneyland.
2. He is super stoked that he will be going with you.
3. Now take all that excitement and turn it into disappointment because this giant wonderful thing has been turned into a kind of dirty trick.
Sorry dude, but to me, you kind of messed up. Why turn what should be a ton of wonderful DISNEY memories into something scary.
I , like another poster said, don't know if you are a bad dad based on this one thing, but I am sure you feel pretty bad.
I have to agree, he may not trust you on the simplest things now. So in the future when you tell him its just a simple ..... and he freaks out, just remember, its on you. So be gentle and forgiving. If you are unable to do that, then , yes, that makes you a bad dad. Sorry to say, but you may have paved a path you will have to be willing to walk on.
To rectify the situation I would just be honest with him. Tell him you messed up. Tell him you thought he could handle it. Tell him its okay that he didnt like it and freaked out. Hes a little boy. And its okay to be scared. An ice cream sundae for dinner and a good shopping trip to the toy store along with a verbal apology is a good start too. And if he is mad at you, let him verbalize it. Let him know its okay to get it off his chest. That way he will know that everyone is allowed to have feelings and work them out.
Good luck!