It sounds like you would like to do this, you are just worried about messing up under pressure. If this is the case - go for it. You already have plenty of good reasons why you would like to do it and some awareness of the negative aspects of exams. Both are quite real. Another thing you need to take into consideration is that you will be playing for somebody who may be kind or very tough in their marking and that is something way outside your control. Sure, there are plenty of pros and cons. You should remember that when / if you do an exam. They are not necessarily fair and true assessments of what you can or can't do - but they do give structure to your work, a reason for that work and hopefully a qualification and formal recognition of what you can do.
I would not worry about getting anxious - everyone does, though some more than others. If you totally mess up an exam it really is not the end of the world - although the disappointment is very real after all that work and you might need to pick yourself up again by remembering the realities go far beyond whether or not you are any good. If you are anxious playing in this kind of situation then the experience is one of the easiest ways of getting used to it and over time reducing such fears.
DO what you have the drive to do. Don't be afraid of it, but don't just do it because you think you 'should'. If you want to, just the work is well worth it.
Consider that if you normally play at an A / distinction level, but you tend to have quite some stress about the situation, you could happily get a pass. If you get better than that you can have a party and be very proud. Use your self-awareness of nerves to temper your self-expectations. Work towards an A level so that even with the nerves you still show proficiency enough to pass - and then you will also have the experience so less to fear if you try again.
Topic: Should I do an exam?