You don't need an excuse. If you're at a party and no longer want to be there, say "I have to go now, thanks for the great party" to the host and leave
No one cares why you're leaving. I'm probably well on the neurotypical end of the spectrum and I'm usually there first in my friend group to leave a party just because parties are late and I wake early. No one complains unless I'm their lift home and they don't want to leave yet
Not how the spectrum works. There's no "neurotypical" end. Assuming we're talking about autism, the spectrum refers to the diversity and expression of symptoms, rather than a gauge between "no autism" and "full autism".
If you meant you are less debilitated by your autism, then the term is "Level 1", which is just low support needs.
I'm personally a fan of the little wheel where you scale your symptoms (idk if that's the right word) 1-5 because even "neurotypical" people will still probably have a 2 or higher in at least one category