Practice it this way
put a C (or anynote) down, and hold, now..... switch fingers on the C in the order 1,2,3,4,4,3,2,1,1,2,3,4,3,2,1 etc...... BUT do not let the not RISE So it stays down, and the fingers keep changing.
Do that, then, start using 1,2,3,3,2,1 but let the note rise and fall sounding at every change. Do it slowly, metromome at 60, 4 notes to a beat, but even. Then notch up the metroneme at will, but keeping even.
Wrist much have the smallest amount of mvt, keep it to an absolute minimum, and hand fairly still. Keep it VERY relaxed, and you can go on for ever, I try to see how long I can last, and I can hit 4 mins easily, then I get bored lol.
It is an essential technique, for pieces like Ravel's Alborado, Liszt Gnomenreigen etc...
As for thumb hitting wrong notes, my only explanation is that you are moving your hand too much, minimal movement. Nver let the note rise fully, you have to find the point where the hammer is just off the string, but only a tap can make it strike, and hold that point with tiny flicks of the fingers. With experience, and when you know the instrument, you get a feel for that point. Like a clutch when driving a car.
As for the 2222 in Scarbo, I was advised to do that too, and I have read my articles about it. The fact is that Ravel's piano action was very light, and that can be noticed by his piano writing, try Albarado Glissando's on a modern piano with heavy action ouch!!!!! But 2222 can be done, with 1 finger repetitions, it's all in the wrist, just as octave repetitions are. The big thing is relxation, and you will know very fast if uyou are not relaxed, you get tense forearms, and you wrist will stop moving.
Hope that helps.
