My rudder is twisted, somewhere along the line it wasn't flat on the beams (in fact the beams themselves weren't flat - see my forum post) and so the final product won't lay flat.
Zentih think the twist is in the bottom ribs so I will start at the bottom and drill out upwards until it lies flat. Depending how far I get I will re-rivet. Or I will get another kit. Coming with no experience of any of the tools and techniques needed for this endeavour, I've learned so much and if this rudder is the throw-away material I learned on, I can live with that.