Been there - had that happen.

How did you lock the crank to do the nut up ?

I found (the hard way) that the only safe way is to raise the barrel & put a hardwood spacer under the piston to do the crank end nut up to the specified torque (around 100NM - see manual). I initially made the mistake of doing mine up in top gear with the back brake on until the clutch slipped, as I didn't have a torque wrench at the time. After the clutch came off (like yours, but several miles from home) I did some checks with a torque wrench (after I bought one ! ) & found that the clutch slips at around half the rated nut tightness. I was not comfortable with the other recommendation of stuffing rope down the plug hole to block the piston - IMO this puts too much load on the piston skirt. Blocking the piston under the skirt as recommended by the factory (there is a drawing for the tool to do this in the manual) puts a compression load on the skirt, not sideways.

I made a dummy bearing to act as a spacer to do the nut up without the clutch cover in place & warmed the brake cleaner degreased clutch centre to just bearably hot with a hot air gun ( a recommendation that came form MZ Rider IIRC) before putting it on the brake cleaner degreased crankshaft & doing the nut up to the rated torque. Let the clutch cool, then remove the nut & spacer & refit the cover with the nut done up to the rated torque again.

The dummy bearing is required to prevent damage to the tacho drive gear that is part of the nut (you know how I know this ! ). Bin the damaged clutch drive plate - you won't satisfactorily repair it so that it drives properly & you run the risk of removing the axial clearance on the drive gear that runs on the crankshaft so the clutch won't disengage if lapping it with grinding paste.

If your engine has been apart before you got the bike, the clutch centre may have had historical damage.

This is an area that, if done correctly, works well - but is very intolerant of any shortcomings in parts or assembly method.

Keep at it - you will get there eventually !

Nigel B.