conch is like the vietnamese word "pho" for me. I know how to pronounce it properly, but something in my brain rebels. So even when I say it properly out loud, in my mind I say it again the way I want to say it. That is to say, "I would like a large bowl of the kontsh foh, please", even as my lips say "I would like a large bowl of the conk fuh, please".
Actually, it can be pronounced either "cong-k" or "con-ch". Wiktionary gives the etymology as "From Latin concha from Ancient Greek κόγχη (konkhē, “mussel”)", so even going back to the origins, both are right!