That's kind of the reason I don't tell people outside of here and my family that I think I'm autistic. What if when I am able to go get a proper diagnosis, I'm just simply weird? With unexplained sensory issues, ugh, hate to start looking all over for an explanation about those things again! I do straddle the fence on some symptoms and I have a much easier time with some things than it seems others do. And moreso, what if along the way I somehow made a bad case for the genuinely autistic? One of the women I have the most respect for is autistic, and I'd hate to think in some way my belief of being autistic hurt her in some way. Bleh, headache!
Outside of that and a hypochondriac or two, I don't think I've ever met somebody who was intentionally masquerading as something else because they were that ashamed of what they were. Not even among the transfolk I've known, they were all quite honest, "yeah, I was born that way, but I feel this way is far more accurate of who I am, and I'm okay with it all around". Which is something else entirely different, but still. I have seen a few wrong diagnosis where people would roll their eyes at their current doctor then go find somebody that knew a bit more what they were doing, but that is different too.