I would say in the planes exercises obviously you didnt got every line to the center, about that, something that i do its i put the tip of the pen on every point that the line is gonna cross and then i start ghosting it, remember to use your shoulder more than the wrist, since what you are doing on every exercises its basically lines, you can keep the movement of your shoulder the same and do it to the speed you find more conformtable. Also something about Technical pens is that you shouldnt use them pointing to the side, you should always grab them as straight as possible otherwise the ink would have problems to come out.

P.S: I am just doing the same exercises so i maybe wrong.