I realised that it perhaps isn't apparent how these work, and as I haven't run them for a long time I haven't explained it this time. So, in case you didn't know, here's how they work.
When you enter a promo code give away you enter for a chance to win 1 of X number of codes that are available. Normally this will be 5 or 10 codes maximum. When all the entries are in I close the draw and then select the winners of the codes at random across everyone who's entered. That way it is as fair as it can be.
I hope that clears up any confusion.