Well in the first place, if the state board told you it wouldn't stand in your way, I would take their word for it over someone who is conducting CNA classes and may not even know.
If the state told you it wouldn't stop you, then believe them.
I do understand your fears.
I assume you told the person teaching CNA classes of your conviction?
Just go somewhere else they are giving CNA classes, register, and start your class.
You can contact the Board again in the meantime.
Obviously YOU CAN become a nurse with a felony conviction or the license applications wouldn't ask that question.
Good Luck! You can do it.