Okay, take a deep breath. Remember that you have talent, and that you are being a brave advocate for that talent whenever you enter a contest or send out a query. Be proud of yourself. Then take another deep breath, and don’t drive yourself crazy with worry about whether you should revise the whole thing again before you send it out.
Repeat above as many times as necessary to get yourself through the day — and your entry postmarked.
And, of course, keep up the good work!