What does the error message say exactly. There are two error messages indicating a failed score submission that I can think of off the top of my head that are caused by completely different things. And your description of the message could fit either one of them.
Also, assuming your scores failed to submit due to a connection issue, if they haven't submitted after around an hour (they will keep retrying for that long), there isn't much you can do. So, since that time has passed, closing the game shouldn't do anything.