Hey man, my real name isn't Johannes, and many people call me this. My mother even calls me by a name which isn't my real name. My relatives are Polish, they call me Jan, my mother, too, Jan or Jannick. Nobody I can think of (except people here on Argonath) calls me by my real name. It's nothing bad to do this, to use another name, and I don't think people will be offended... people don't care. You can call yourself Gandhi and people will not mind.... I've friends who call me the name in their language (Juan, Ivan, etc.). Don't worry about it, people think no less of you.
-Jan, Jannick, Johannes, John, OI! You!, Barry