How can I suggest to my psychiatrist that I should have my prescription raised?

You really need to be able to talk to your psychiatrist about anything. He may decide to change your meds, if 20 mgs isn't working anymore, what happens when 40 isn' t and then when 60 doesn't? He will know what to do. Tell him you took a second one by mistake, and noticed you felt so good you counted the rest of your bottle and you had taken 2.