When you pull out the incorrect bid from your box, immediately call the Director.  There is no such thing as a 'Mechanical Error' -it is known as an Unintended Call.  The Director will ask you about your intentions when you made the bid and make a decision.

 More Tournament Director’s Tips 
trowBRIDGEclub - Conduct and Etiquette

 Who me?

Law 74 covers Conduct and Etiquette

Below are some examples of behaviour we hope does not happen at your table.
 

• Asking about a bid (whether alerted or not) for interest, not so that you can decide about your next call.
   
• Getting excited about Partner’s failure to alert or announce the convention you have remembered.
   
• Placing the bidding card down in a meaningful manner to ensure partner realises its significance.
   
• Volunteering information about a bid when you have not been asked.
   
• Stop card a). Forgetting to play it, or not displaying it clearly for about 10 seconds.
   
• Stop card b) Not waiting for about 10 seconds before making a call after a jump bid, irrespective of whether the Stop card has been displayed properly.
   
• Showing dismay or approval at partner’s choice of bid or card play.
   
• Assuming (by putting bidding cards away) that once game is bid the auction ends. There could be a sacrifice or ‘double’ or partner may go onto a Slam, unless you tell him not to!
   
• Playing a card from dummy before declarer calls for it – including a singleton
   
• Detaching a card before it is your turn to play.
   
• Playing off known winners instead of claiming, for the purpose of disconcerting an opponent. (“to prolong play unnecessarily” is a breach of the Laws)
   
• Discussing a hand from the previous round and failing to greet your new opponents
   
• It is poor behaviour to berate partner when he or she plays less than perfectly. Likewise, it is not proper to chastise the opponents when a poor play turns out to be lucky or a good play provides you with a bad board