I was screwing up left and right when I took my instrument checkride years ago and realized it. I decided to do a full stop and sit at the hold short line composing myself for a while before launching for the final approach. This is the only reason I passed.

I learned some good things that day. 1) Your instructor feels you're ready enough to endorse you for a checkride you're probably ready. 2) You can only know so much. Knowing where to find stuff is often a better route to take. 3) If you don't know it the night before the checkride, you're not going to learn it.

Since this realization I have used this method. Study my butt off until two days before. That night, get all of my paperwork and planning together. The night before the checkride, iorn my pants and shirt and then have a beer to help get a solid 8 hours of sleep. Has worked on every stage check and FAA checkride since.