Welcome to our forum!
That's a curious moral dilema you have presented. I would say it was wrong to mislead them, or more accurately, to allow them to be misled when it was in your power to speak the truth. Why did you do that? What were you hoping to gain by not being open and honest?
But on the other hand, we all wear masks to one degree or another in this life, don't we? Who could be totally and transparently honest in all things? Even if we tried, we would inevitably be misunderstood, and in some cases and places, that could even be fatal! So there is much wisdom in silence. You do not owe it to anyone to expose all your inner thoughts. But on the same token, your integrity should start complaining if you wilfully deceive people.
As for dropping a link to you non-Christian site on a Christian forum? That sounds like a very rude thing to do, and probably ineffective since they would likely just delete it and ban you. So why would you want to do that?
If I were you, I imagine I would probably try to gently introduce my "true self" and see if there is anyone there interested in authenticity. If not, I'd say "I'm really sorry for lying to you all" and leave quietly I guess. But this is all hypothetical since I don't know the details of your situation.
Anyway, I hope that helps.
All the best,