Well, that is quite difficult and a constant responsibility. Try to manage it over the internet and may get through it however, during your studies i would recommend you should try not to get involved in something like this.
You always have doubts in things that you are doing. You may think may be it wasn't the best idea. It is really an instinct. But Your fate will always take you where you belong.
I think you should give a writing sample. There is no loss in giving one. An extra documents is usually not a problem however, it can be a positive thing in your part.
These things happen quite often. It happened to me once as well. Its nothing to worry about. Such small errors are often neglected or ignored. It probably will not be a problem.
Well, relevancy is always required. However, depending upon the quality of work you may get an edge. Do try to write and submit relevant papers because you can never be too sure of what is being required here and irrelevant work maybe a negative point.
You can find great samples by searching. Search for images you will see the whole sample and also compare a few to make a good one of your one. Good luck.