The first thing is calling the penalty on yourself is the correct thing to do always. At golf's core are values of honesty, being a gentleman, and fair play. In a competition, since someone can not monitor each individual playing at all times, it is assumed that every one will do the right thing. Should you knowingly try to get away with something less, your reputation would suffer great harm both on an off the course amongst your friends and fellow golfer's.

That said, I feel the penalty for playing a complete round with too many clubs would probably be more substantial than what you think unless there were some local rules for your competition in effect.

Good luck, you will at least know you did the right thing.
Bob