If you expect everything to be flawless, you're familiar with perfectionism. Your perfectionism means any grade less than 100% makes you feel disappointed. You shouldn't be so hard on yourself!
Perfectionism means you have extremely high — even impossible — standards. Your perfectionism might be self-focused, all about setting high goals and being critical of yourself when you don't quite achieve them. Some people hold others to these standard, their perfectionism leading them to expect impeccable work from everyone: "My piano teacher's perfectionism can be stressful. One wrong note and I have to start the whole piece over."