The incorrect piece of information is:
"The spot marked 'maximum gravitational potential energy' should be on the lowest point of the roller coaster, at the far left side on the bottom."
This statement is wrong because maximum gravitational potential energy occurs at the highest point of the roller coaster, not the lowest point. At the lowest point, the roller coaster would have maximum kinetic energy instead, as the potential energy is converted into kinetic energy during the descent.