All rookies are expected to make mental mistakes in preseason, even 1st round draft picks.
And mental mistakes are some of the most correctable.
In fact you even see veterans make those mistakes in the regular season, with penalties, and bounces balls. It's pretty common.
In fact, he showed some rare mature and veteran qualities, after he made the mistakes, by that "short-term memory" and strong confidence, by immediately bouncing back with great plays after the mistakes.
If he hasn't done enough to make the team, I'm not sure what he has to do ? Perfection ?