No matter what you or your OCS class does or how well you believe it to be done, the Chiefs and DIs will find something wrong with it. Your life at OCS will become "easier" the moment you embrace this fact. Realize that 100 percent effort from you does not require a pat on the back or a "Good Job Slugger, keep up the work." The sooner this happens, you will start noticing time moves more fluidly.
Closely related to that is, stop worrying about trying to avoid getting RPTed (obviously within reason, make sure to adhere to rules/policies and be respectful, etc.), there will simply be times where you will be in the wrong place at the wrong time or a DI is bored and you will enjoy some minutes of fun.
Simulated stress at OCS will still cause you to have your moments of freaking out and "what the hell is the point of this," but always keep your eye on the prize.