Pretty rare that a clutch goes - did you just pick up the 6MT X or have you had it for a while?
Anyway, have you tried the dealer to source the clutch kit for you? If RockAuto is giving you the wrong part, send it back and get your money back - for your 6MT I'm finding part #
21207546378 - did that part cross reference with the Luk kit you bought from RockAuto?
You can get the Luk kit or Genuine BMW kit for $20 more
https://www.ecstuning.com/Search/Sit...h/21207546378/