Everyone feels like an idiot after their exam. I thought I might have failed right up until I saw my score.
Keep in mind - a passing score is probably less % correct than on a normal class exam, so it's hard to have a feel for how well you did. Also you probably remember the questions you struggled with or weren't sure about more than you remember ones you aced.
Try not to dwell on it too much. All you can do is wait for your score.