To the OP:
I've felt the same way, though I referred to it as "not feeling autistic enough."
I got my dx 10 months ago. I've had only one meltdown: preschool age in response to noise. I've never had a shutdown. I've never had a burnout (because apparently, risk of burnout has a linear association to extent of masking -- and I've never masked beyond just slightly).
I also keep thinking that some of my traits were developed in response to the environment I grew up in.
But I have to keep reassuring myself that I AM autistic -- by using some tricks up my sleeve -- and perhaps they will help you.
1) What traits or features do you have that ONLY autism can explain? In my case it's stimming (a LOT including rocking), hyperfixated interests, avoidance of small-talk, tendency towards literal thinking, extensive (and I' mean EXTENSIVE) rehearsing in my head of anticipated interactions with people, which include the use of imaginary or "sample" people), preference for sameness, need to always plan, odd AF sensory issues. No other diagnosis explains all of these. Neither does being picked on by teachers in high school or made fun of by classmates in grade school and high school.
2) Invest in insight therapy. Have a list of questions ready. I had teleconferences with a psych who was with the clinic I got my dx from. I asked her straight out what about me, as we interacted, might indicate autism. She said that whenever we began our sessions, I never engaged in small-talk, and instead I dove right in. She also said that I was pretty matter-of-fact with everything and almost had a flat affect.