The loss of the Queen can have more of a pysological effect than anything else, especially if both opponents are reasonably matched.

Very much like missing a putt in golf, the key is to forget what has happened and concentrate on what to do next. You can analyze your mistake later, and you should, but for now readjust your strategy.

Try to restrict the opponents Queens movement where possible, especially if it is early in the game. Proceed with care and try not move a piece needlesly.

Just don't give up and learn from your mistake.