How do I explain that to my parents?

So, most of the time when we speak about me being autistic or autism in general, they bring up me being only “a little autistic” or ___ and ___ being “really autistic”.

I nicely explained to them several times that it’s a spectrum and that there’s nothing like being a little or a lot autistic. I know my mom doesn’t mean it in a bad way and that she’s really trying to understand and remember but my dad doesn’t want to accept that I’m actually disabled/autistic. I’d like to explain it to them in a way that they can understand/accept it better because maybe I’m doing something wrong explaining. I thought maybe someone has an idea how I could explain it to them.

(Please excuse any grammar or vocabulary mistakes. English isn’t my native language)