Ask: Is "the script is written" literal?
“Is the Course saying that the script is written and our only choice is to see everything with the ego or the Holy Spirit? Or is it saying that in every situation where we make a decision the script switches to a different script?” – BM
A Course in Miracles is saying everything that happens is already set and your choice is in how you see it.
Although you feel that your desires, motivations, choices, and actions are your own, really you are a part of a whole, and that whole lives through you, showing up as your desires, motivations, choices and actions. While your will feels free, it is really part of a greater will living through you.
To understand this, you must understand the nature of what you perceive as reality, or the world you live in. It is actually an instant of undoing unfolding as time. That instant is the idea of not-God (not-Truth) arising and being undone in the Mind of God (Truth). God, being All, must contain the idea of Its Own opposite. But being All, God cannot have an opposite. God’s all-encompassing nature undoes the idea of not-God the instant it arises. It is as though God thought, “What’s my opposite? Oh, yeah, I can’t have an opposite.” And the idea was done.
But within the idea of not-God—but not in God—it seems as though the opposite of God occurred. God is Formless, Timeless, and Infinite. So not-God is time bound, limited form. Time is the illusion on which all other illusions rest. Within the idea of not-God it seems as though the idea of not-God arose long ago and will be undone in some indefinite future.
Since God is All, God is Reality. What you experience as a world in time is really a pseudo-reality. It is just a story of the Undoing (the Atonement in ACIM) of the idea of not-God. So the outcome is inevitable and everything that happens, no matter how it appears at any given moment, is part of the Undoing, and everyone is playing their part perfectly.
“The time is set already. It appears to be quite arbitrary. Yet there is no step along the road that anyone takes but by chance. It has already been taken by him, although he has not yet embarked on it. For time but seems to go in one direction. We but undertake a journey that is over. Yet it seems to have a future still unknown to us.
Time is a trick, a sleight of hand, a vast illusion in which figures come and go as if by magic. Yet there is a plan behind appearances that does not change. The script is written. When experience will come to end your doubting has been set. For we but see the journey from the point at which it ended, looking back on it, imagining we make it once again; reviewing mentally what has gone by.” (W-158.3-4) (my bold)
What you “review” is the undoing itself, not the details unfolding in time. In time, there is cause and effect, with some effects being also causes. But it all leads to an inevitable end, just as when you watch a movie the ending is already set. So when you get caught up in what is appearing at any given moment, you can remember that there is a happy ending, no matter all the drama that gets the story there!