Heya fufufan,
First of all, welcome!
Second of all, it seems like when you are doing the pen control exercises you trying to be careful. This is going to sound unintuitive but you want to be faster with your strokes. This is because faster strokes turn out smoother It's going to be difficult at first because of how inaccurate your strokes will become, but after sustained practice your lines will become smooth and accurate.
Also, I want to ask: have you been taught to draw from your shoulder and elbow instead of your wrist? If you draw solely from your wrist I recommend you to try using your elbow and shoulder too.
This is a great effort! Keep it up!
