Thanks!,
I figured out the reason for the 'bent' stringer:
I'd made copies of the original plan on smaller sheets, luckily at 100%, so scale was still right.
I built the fuselage in two runs (my cardboard underlayment was a bit small).
Apparently I did not properly line up for the rear half and placed the second support behind the canopy slanting forward.
This caused the holes for the stringers to not line up.
Well, this is my second balsa built ever and the last one was over 20 years ago (tiger moth), so it is not too bad
BTW what would be better (weight wise): use the paper that came with the kit and use the 'shrinking lacker' (don't know the english for it, we call it 'spanlak')
or go with monokote or something similar (kind of removes the warbird look I guess)?