I think you have to just get over it, not everyone is perfect. or maybe if you feel you did better you can get a remark? a B doesnt make you unintelligent, just keep telling yourself that. if it does then im as thick as two short planks...
basically, has not getting an A stopped you from doing anything, like have you been rejected from uni or something? i did my a levels a couple of years ago and was devastated when i didnt get an A in my french, just because one module's marks were very low, and i worked really hard, but really, i thought a b is not gonna kill me or stop me from doing what i want to do. being a perfectionist 100% of the time isnt good for you.