Graham Poll once gave a player 3 yellow cards. Howard Webb didn't send off Nigel De Jong in the World Cup final for a karate kick to the chest. Keith Stroud gave an IDFK after encroachment at a penalty instead of a retake. Even referees with decades of experience, who are notionally at the top of their profession make bad decisions. Do not be too hard on yourself for making mistakes in your first game. You did plenty right, and as others have said it is helpful to write those things down after each game so you can see what you do well, not just what you need to improve on.