Whatever it is that is bothering you now: Never be upset that it didn’t work out. Be glad that you learned something to make you better for the next time.
Prophet (salallahu alayhi wa sallam) said: Know that if the nation were to gather together to benefit you with anything, they would not benefit you except with what Allah had already prescribed for you. And if they were to gather together to harm you with anything, they would not harm you except with what Allah had already prescribed against you. The pens have been lifted and the pages have dried.” (Tirmidhi)