It seems to me that the advice you are getting is from people giving you advice on the phone and not really representing you.
I don't think claiming ignorance, even if true, works for getting out of misrepresentation and fraud. Particularly in this administration. I wouldn't trust any advice you are being given by someone who is not representing you or has not 'won' cases involving misrepresentation or has knowledge of muslim customs.
The only idea I have is to try to find some professors of law in your country or in the US (who know about muslim law?) who can write about how this paperwork or ceremony is not viewed as marriage in your country. Maybe trying to explain it is a gray area works. Then you could have this religious officiant say he thinks the paperwork counts as marriage, but if you could find another who thinks it doesn't (not sure this is possible), then that could help you.
I honestly don't understand all of these customs, but I don't think saying "We thought doing this ceremony was not marriage, but when I realized we were married, instead of leaving and doing a marriage visa, I tried to fix it retroactively" is enough. Plus, it's been like 2 years since he came to the US on a K1 and you never married. If you truly thought it was not an official marriage, you could have asked another religious officiant or just marry in the court house.