You are not a stupid f*** up! I make mistakes too and sometimes feel like beating myself up about it. But, I try to remember that everybody does and to think of the things I do well too. It makes me feel sad to see you so hard on yourself. You care about your job - that is obvious from how hard you are being on yourself. You could always just apologise to your boss for the mistake - but, don't be too apologetic!! It sounds like a mistake anyone could make.