Hang on! Do you mean that the note you pulled off onto - and not the one you actually tapped - rang out? if it's just the one you tapped then surely it isn't too hard to release the pressure to kill the note?
this is the kind of question it would be easier to answer if you provided a tab for and mark where you have a problem. That said, Chopin sound bloody ambitious to me and i might not have anything helpful to say..