I would have used alot more water and instead of pressing it flat overnight or whatever.......overbend it a good bit. I would also make it wet enough,or keep re-wetting it(dont be afraid to use alot of water) so that it can soak into the wood good (maybe 1/2 hour,45min) then while its over bend dry it with a heat gun good. This is how I always form my sheet balsa when doing contours and it works great.

And yes,I've always found that if pieces bowed in opposite directions will cancel each other out as long as they are close to the same density. Keep us posted!