You had two years to prepare. You didn't. Every time you sit down now, the weight of what you didn't do drops on top of what you're about to do, and the chair becomes impossible to stay in. So you check your phone, and the loop restarts.
This is not laziness. This is a specific mechanism the brain runs when past failure contaminates present action, and the more you care about the goal, the worse it gets.
What is actually happening
The feeling you are describing is what researchers call self-referential rumination around past failure. It is not the same as ordinary procrastination, which is primarily about avoiding a present negative emotion. Rumination about regret is about reliving the past failure every time the goal comes back into focus. That reliving is itself aversive, so the brain flinches away from any stimulus that triggers it, including the goal.
Timothy Pychyl's research at Carleton University on procrastination established that the function of avoidance is short-term mood repair (*Sirois & Pychyl, 2013 - "Procrastination and the Priority of Short-Term Mood Regulation"*). When the goal is also a site of unprocessed regret, opening the book does not only expose you to the hard task. It exposes you to the full accounting of every day you didn't open it. Avoidance is how the nervous system protects itself from a compound hit.
The second layer is what Kristin Neff calls the self-criticism trap (*Neff, 2003 - "Self-Compassion: An Alternative Conceptualization"*). Harsh self-judgment does not motivate. It activates the same threat response as external criticism, which depletes the very executive resources you need to actually sit down and study. You cannot shame yourself into the work. The shame is part of what is blocking you.
So the "discipline" frame is the wrong frame. You do not need to try harder. You need to break the contamination.