When you get stuck, go back by the type of sound, not by the symptom. If you cannot say q, then before drilling q on its own, check the tongue position, the air, and the pairing with ü. This index is the way into the chapter you need.
Once you have reread the chapter you found here, record just one practice word. Narrow down what to fix, and two days later record the same word again to compare — that is how a lesson you return to actually stays with you.