Quick Thought: No One Cares How Little Rehearsal You Had
I promise that no one on the bandstand or in audience that's gonna move your career forward is thinking, "That cat sounds great for not knowing the songs and bullshitting through it."
Maybe it's short notice. Maybe you had some stuff come up. If you want to move upwards, find the time and learn the songs before the show. 5 years from now you'll thank me.