I am in no way a lawyer. If I had to guess, I'd say you're most likely out of luck. I think it's generally considered common knowledge (factual information beyond dispute that one could easily look up) that Megan's Law created a list of sex offenders that anyone can access online. Of course I could be wrong here, but I don't think saying you were "deceived" is the same as you simply not knowing all registered sex offenders are listed online.
The smartest thing for you to do, I think, would be to speak with a new lawyer in your area. I would have to assume that unless you have other solid evidence that your counsel deceived or wrongly pushed you into accepting the defendant's plea, there probably isn't much you can do. Though all states are different, a lawyer, after considering everything you've told them, might tell you to file a motion to reopen the case with the court and see where that takes you. I was reading online, too, that while the case might not be reopened, the outcome could be argued again in front of a judge.
This link hopefully can help explain more about a motion to reopen a case in search of a new outcome:
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