Background
I am an undergraduate and I have just finished my first calculus class (Calc I) this summer. While this class has gone very well for me by any objective standard, I find myself drifting towards a pathological obsession with perfection. This manifests itself primarily on tests where I feel compelled to get a perfect score to even consider that particular test as a success. Getting something like a 96 has begun to feel as if I'd received a 40. While I find calculus to come very naturally to me conceptually, I am somewhat prone to making minor computational errors (i.e. I'm not a human computer) and thus, I find it difficult to attain the level of perfection that I expect of myself. My test average is about a 96 which my rational self can recognize as "good" but my emotional self interprets as a crushing blow, especially when it was such a simple error that kept me from a perfect score.
Now, despite all of this, I still very much love mathematics in the sense that it is the only thing I've ever experienced academically that brings me intrinsic joy. I spend a good deal (at least 3-4 hrs./day) of my time learning mathematics on my own just because I want to know it. As such, I'd consider myself fairly advanced and mathematically mature for where I am in my formal academic progression. Rationally, I realize that real mathematics is generally invariant under computational errors but I still feel as if any error somehow compromises my credibility. It has come to the point where I've finally swallowed my pride and seen a therapist who encouraged me to reach out to some mathematicians or students of mathematics in general who have struggled with similar perfectionistic tendencies. I am mortified at the thought of laying all of this on one of my flesh and blood professors so I am hoping that this post might serve as a proxy.
Note: I realize posts like this are generally frowned upon but I really have no alternative. To keep this somewhat within the bounds of the guidelines, I am NOT interested in a debate about various schools of psychology or really any psychology for that matter. I'm more looking for personal anecdotal strategies for overcoming perfectionism, relevant historical anecdotes (I feel like mathematics self-selects for perfectionism), etc. If this gets closed/deleted then I understand but hopefully there is a place for this question somewhere on this site.
I'm a perfectionist, but I unintentionally make lots of careless mistakes all the time. Like you, I feel a sharp twinge of disappointment or embarrassment, depending on the situation, but it goes away almost immediately. The reason is that I consider intention and not outcome to be the deciding factor, and so as long as I had put in what I deem sufficient effort to avoid careless mistakes (such as checking my work), whether I actually make mistakes will be irrelevant to my judgement of myself. This is why I can justify and succeed in suppressing any feeling of chagrin quickly if there was no reasonable way I could have prevented some mistake.
Of course, being a perfectionist, I would still attempt to fix any mistake I am made aware of in as perfect manner as possible. This can be a second avenue for you to channel your thoughts and energy into; instead of harping on your failure to yourself you could focus on rectifying the fault. This includes trying to figure out ways to prevent subsequent recurrence of the same situation that encourages mistakes (such as tiredness, distractions, style of working, ...) as well as actually fixing the consequences of your fault (wrong computation? do it right this time! claimed a false statement to someone? make a corrected statement!).
Note that my advice applies to all areas of life and not just mathematics. That said, some people may find it harder to adopt this attitude than others. Do not be afraid to recognize that, and also know that different people may find different ways of de-stressing to be effective. Yes, extreme perfectionism leads to an unhealthy level of stress, so we should both regulate our perfectionism and also have an outlet to release perfectionism-driven stress. Also do not be concerned about how others think of you when you seek help. After all, nearly everyone has to rely on others for various things, and social interaction is one of them.
After seeing Jack D'Aurizio's comment, I would like to add that you should also learn to see mathematics (like many other fields) as a cooperative endeavour. It is not only easier to work together than alone, it is easier to help each other spot and fix mistakes.