Welcome to English. There is only one person in the world who speaks perfect English: Queen Elizabeth II. It is her English, everybody else tries to speak the Queen's English, speaks it well, or can't speak it right, according to somebody, and it goes downhill the more removed from the source. As a Professor of English from Colorado, America, and an Oral Examiner for Cambridge University (in England) for first and advanced certificates of English, I know something about encountering the glitches. Don't feel bad about it, it's part of what others dare to call "mistake"; it's your education, we make jokes about it. The important thing to remember is that understanding is key, everything else is not that important. If I were you I would have some fun with it. The differences are not significant in most situations. The Brits complain that the Yankees can't speak English right, the Spanish complain that Mexicans can't speak their language right, the Portuguese complain about the Brazilians, the French complain that the Canadians can't speak French right, The most important thing is this: language is a tool for making yourself understood and to understand the other person. There is only one rule: Understanding. Everything else is second in importance. Good Q. Happy hunting.