I knew someone who was TA'ing a class back when they were in grad school. I heard a story about him - to get ahead of this uncertainty he gave the class three options for what to call him:
1) 'Steve' (his first name)
2) 'Mr. Wolfman' (his last name)
3) 'Darth Wolfman' (funny, obvious not meant to be taken seriously, option)
I don't think you should feel awkward. I refer to all my teachers in emails as professor ( unless I want to list more detailed honorifics ). My current analytics guy is clearly very smart, seems to be in that adjunct zone, but I address him as professor out of sheer respect.
Them: "Hello Professor"
Me: "Technically I'm not a professor."
Them: "Okay, we'll just call you Doctor."
Me: "Yeah, about that... not a doctor either."
Them: "So why are we paying you?"
Me: "Technically, you're paying the school. And the school is paying me... very little"
Them: "Answer the question"
Me: "Because I know stuff that you don't."
Mostly they still just call me professor and I feel awkward every time.