It's quite alright. Everybody's ignorant about something. The trick is to not pretend to know more than you do.
Not sure I understand your question. Critias is part of a group of works by Plato framing a political and philosophical idea via a fictional discussion between philosophers, one of whom brings up Atlantis although no one else in the discussion has a clue of what he's talking about. Have you read it? It's quite clear that it's a narrative device and not a history lesson by the author.
In any case, EVEN IF Plato had flat out claimed that Atlantis was a real place, we have only his word, and absolutely no evidence to confirm it. You also don't have evidence, only a very generous interpretation of a single symbol.