ORIGINAL: Mr Cox
Sounds like the angle of attack on the wing is simply too high or the wing is loose, but 10 rubber bands ought to be enough...
How did you measure the angle of incidence, it can be tricky to get the correct angle measure on a flat bottom wing as it is highly dependent on the profile of the leading edge. I would just shim the trailing edge until it flies well.
I used a Robart incidence meter. And since it is a semi-symmetrical wing I measured it at several points along the wing to compensate for any leading edge irregularities.
I think I will shim it closer to +1° for the next flight.