Look back at what you wrote while reading.
Many pages asked you for a line: a dream, a self you caught, a moment of fear, a kindness given, a scene that keeps returning. If you wrote them, you now hold a second book. It is the record of your own work, and nobody else could have written it.
Read it from the beginning. Notice how the early lines sound. Notice what you saw in the first weeks that you can barely see now, because it has changed. Notice what still comes back, line after line. That is where your work is now.
If you did not write much, that is fine too. Begin now. One line a day from here on is enough.
This is the deepest reason the book asked you to write. It was never to grade you. Nothing here is counted or checked. It was so that you could see, with your own eyes, that you are changing. Belief is not needed for that. Your own lines are the proof.