The only native English word with a phonemic glottal stop, uh-uh, includes it in the spelling, for obvious reasons. You could write ah-ah, or a-a, on that model, but this isn't done.
> But 'A'ā isn’t the right kind of correct either?
That preserves a bunch of information that can't exist in English regardless of how you write it.
"Aa" does the opposite, erasing information that is critical to the pronunciation of the word. There is no way to read "aa" as being more than one syllable long.
The only native English word with a phonemic glottal stop, uh-uh, includes it in the spelling, for obvious reasons. You could write ah-ah, or a-a, on that model, but this isn't done.