Spooks - if you get stuck on a place in the song, and mentally/psychologically freak out at a spot or several spots in a song, play/sing through the spot(s) slowly, always perfectly, just as slow as you need to get it right! Speed is not the issue if this is your type of problem; it is smoothing out the anticipation of a mess up. So, we're trying to get your confidence back so that you can do that part right!
2 weeks before the performance play/sing the song just once, once each 2 hours. Don't practice; just do the song once. Go about your day.