Focusing too much on scores/results can cause the anxiety felt by all of us periodically. My suggestion would be to focus on making shots, one at a time, and finding contentment in the process. "Fear based" bowling will never produce consistent results, and your self esteem should never be attached to your bowling scores for the night.
Find something positive from every shot and dwell "there" instead of the pin/pins that didn't go down and how robbed you were... You can train your mind to relax and think positively. I, for example, have told myself "okay that shot was HORRIBLE, but at least I'm left with an easy spare", and so on.
Once you become "the captain of your own ship" and control the emotions the scores will inevitably follow. Good luck to you.