Instead of talking about what you shouldn't give in to on the course, learn what the opposition would be and work to choose it. Your belief that your emotions are natural reactions to your play might be the very thing holding you back.
The most commonly used negative emotion I hear as a coach is frustration. Players seem to accept that frustration is a natural experience on the golf course. Instead of choosing to feel frustration after a missed putt or the feeling of no control, you can instead choose emotions such as patience, acceptance or trust. Many players feel disgust with their inability to execute a shot or control their focus. Disgust or showing contempt for yourself pits you against yourself. On the course, you need to be your own coach and you would never choose a coach who was disgusted by your behavior. Instead, you would choose a ccoach who was optimistic and interested in your play. Perhaps the toughest emotion to handle as a competitor is sadness. It is debilitating and causes players to give up on themselves. Learning to find joy on any given day is truly a gift to a competitive golfer. The joy must be found in the playing, the camaraderie, the nature or the anticipation. It cannot be reliant upon only results. The final emotion I see often is fear. While the opposite of fear seems to be brave, in golf I believe it is closer to what we all seek, which is confidence. The understanding that your confidence is a choice, as is fear is an important lesson that competitive golfers need to learn.
Here is a great article on fear vs. confidence by climber Whitney Boland. It works perfectly for golf, too.
Remember, your emotions lead your thoughts and actions, so don't give in to negative emotions. Instead, keep a positive mental attitude throughout your day.