When you learn a new language and speak to native speakers for the first few times, you sometimes have the impression that you are pronouncing well, repeating sound by sound what you have learned in class. Unfortunately, the person you’re talking to doesn’t always understand.
I guess that’s what happened to poor Mark Twain who prefers to accuse the French of not understanding him rather than questioning his ability to speak the French language well.
Don’t worry! Don’t be discouraged! Keep pronouncing as best you can and keep improving by practising.