A similar one that I used to get wrong all the time is empanada. No ñ in that either, but I always said em-puh-NYAH-duh. Then one day I noticed it was just a regular n and it is pronouced em-puh-NAH-duh.
Now for a really embarrassing one. This was back in the day when I was working with my friend and colleague Alan Cooper (of interaction design fame) on what became Visual Basic. We were on a phone call and I said something about a zhuh-NAIR of music. Alan asked "what's that?" I explained that it was like a category or a particular style. He said "do you mean ZHAHN-ruh?"
It's funny how these embarrassing moments stick in your brain. I could tell you exactly where I was, and even which direction I was facing when we had that conversation.
But I was grateful that Alan corrected me and I won't sound like a fool any more when I talk about a genre.
I had one friend who would never gracefully accept a correction like that. One time he told me about a neighbor who "took his dog to the pond." I said "that's nice, does the dog like to go swimming?" He said "no, the POND, the place where they put dogs to sleep."
He went through his whole life mispronouncing "dog pound", and many, many other words.