It’s not likely, but if you find something that’s just wrong, then own up to it. Don’t lead with it in the viva, but go prepared. Make notes and figure out what would make it right. You don’t need to be perfect, you don’t need to have all the answers, but you can go with a sense of what you need to explain and explore things with your examiners.
Wrong doesn’t automatically mean you fail. Just because something isn’t right in your research, it doesn’t mean there’s something wrong with you.