That sounds incredibly frustrating
If nothing else (and I hope there is more to the "else") I have learned that when I self-report through assessments, I do not do justice to my distress. So even some types of written communication, such as a provided list of options, leave me muted. In the event that I need to seek out a second opinion, I will say this much at the outset. Though I suppose saying this throws the dataset into doubt, so I don't know if an assessor will be please to hear my insights.
That label "high functioning" or "too high functioning" makes me want to bang my head against a wall. "Too adaptable to be noticed" seems somewhat more fitting, though it still does not address the level of distress.
What I dread is people who will say, "Yeah I didn't think you were autistic" and basically validate themselves at me. I don't know what I will do then, other than shut down completely.
How do you handle your certainty of self-diagnosis with a document that disagrees?
The last time I saw any sort of mental health professional was years ago, and I didn't even understand what was going on myself - I was experiencing a bunch of things that I didn't realize weren't normal experiences - I thought my problem was that things were more difficult for me to experience than they were for others, not that others genuinely didn't have those experiences in the first place. (This is especially notable with sensory issues - I wondered how people didn't react the way I did without realizing that they genuinely weren't having the same experience. As a result I thought I was "weak" because I couldn't handle it. I hadn't considered that others weren't experiencing the same thing, and if they were, they would react the same way.)
As for how I handle not having a professional diagnosis of autism (and a string of other diagnoses that are wrong and at some points have done far more harm than good) - it's so blatantly obvious at this point that I'm autistic (and have been my entire life...looking back at my childhood I keep thinking "How did they miss THAT?") that there's really no questioning it. The sky is blue (duh) and I'm autistic. I've also come to the conclusion that it really doesn't matter if I have a professional diagnosis or not - a professional diagnosis isn't going to open a lot of doors for me; it will give me more credibility in certain discussions, but credibility isn't important enough for me to go through the arduous process (and pay a large amount of money) to get a professional diagnosis. Going through years of waiting, hours of evaluations and possibly thousands of dollars just isn't worth it to win an argument.
The autistic community has been totally awesome about making the resources that I really need (knowledge and community) freely available, thereby removing the need to involve professionals and their opinions for most things. My main frustration at this point is that I wasn't diagnosed much sooner because I could have had these things earlier (possibly - in some ways, when I was a child/teenager that knowledge and community didn't exist to begin with, so it's entirely possible I would not have had access to it regardless).
People didn't want to "label" me or "pathologize" me, without understanding that if I wasn't autistic, I got to be all sorts of other things (weak, lazy, dramatic, psychotic, crazy, "no people skills") and that, not being permitted to have answers from good, solid sources I sought them from other places which were not very good or helpful at all and exacerbated all of the things that caused me so much trouble in the first place, as well as causing other problems. Because I have always been searching for answers, that's something I don't think I'll ever be able to stop doing. (There's an incredibly frustrating thing that goes along with this if I say I'm autistic or explain my autistic traits in certain circles - people immediately start trying to make me feel better about them, or talk me out of them, or tell me "it's not anything to worry about" etc. I know these people mean the best, but it really sounds like "don't worry, being you isn't a bad thing!" and that's just downright offensive.)
Probably one of the best things I've learned how to do (and at times I am still working on this...practice makes perfect!) is to roll my eyes, shake my head and move on with life, having decided that the person speaking has no clue what they're talking about when they start with that crap. Because I know who I am and what I need...and oftentimes it's up to me to make that happen because, as much as I really want to be understood by those close to me (and it freaking HURTS when the people I care most about don't understand me!) there's a good chance they never will, and I have to make peace with that.