That's where you're going wrong.
The big (27mm?) clutch centre nut is done up to a very high setting; the ones that hold the clutch pressure plate on are only a fraction of that, just normal tight with a spanner.
No call at all for a breaker bar for those, a 1/4" socket set is more than enough.
Same for the ones holding the clutch cover on, and waterpump.
Read your Haynes more carefully, and identify the correct bolts by using the parts lists with diagrams in the sticky threads in the Workshop section.
It's not falling off, it's an upgrade opportunity.