First off, you are most likely not in the top players at these tournys... right? I figure that the top guys are shooting around 75 consistently??
WHich is probably making you a little intimidated and looking at other players before tee off. What I would recommend is of course taking one shot at a time, with a consistent preshot routine, and not worrying about anyone except yourself before tee off and even during the round. You sound like some of my friends in highschool... they did the same thing you are doing.
Since you said that your entire game is affected, then most likely you are overly stressed and worried about your score. Just make sure to relax before each shot and concentrate on your target.
Good luck