I studied really hard for a test, I ended up getting an 84 when I was aiming for 90+

I truly understand your frustration. Maybe try a different approach, think of your studying not for the grade, but for the knowledge. There will never be anything wrong with reading, thinking of and learning any topic when you goal is just to be smarter and more informed about the subject. The grades do have their importance, but the most important is what you learn and how you can apply it later in life.

Also, even with good grades often a teacher or tutor may be able to offer some helpful advice, certainly more than what you will likely find here anyway.

You got good grades at first place. Secondly, in my experience those who got higher numbers, know the trick to attempt the exam papers but they might not be able to teach people. Most importantly, grades won't help in practical life but know it better will.

Try to relax. If you know the material there is no need to study more. Take a day or two off before the test and ace it when you are relaxed and not stressed.

Perfectionism isn't a helpful trait

Why?