Sounds like you've got yourself a nasty case of "Imposter Syndrome". Don't worry, it's not permanent or fatal!
Nearly everyone gets it during the early stages of recognition, and sometimes even after diagnosis (it's been over 3 years since I was diagnosed, and it still niggles at me now and then.) Years of masking make it worse, I think, because you end up with two versions of yourself; "safe place version" with lots of autistic traits, and "someone's watching version" which has more "normal" behaviour - and people constantly tell you that the "someone's watching version" is the one that you should aspire to be, or even the one that you really are.
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When you are fighting an invisible monster, first throw a bucket of paint over it.