Can you go back to step 1? That is, remove the floats and put wheels back on and see how the planes acts. If the trouble goes away, the problem is in the float instalation. If it remains, it's with the plane itself. Perhaps with the engine instalation. The engine should not have left thrust. I'm not sure what you mean that the floats are perpendicular. They should be parallel to each other and have a slight negative incedence to the plane. That is, the float tips should be slightly lower that the tails, but only a degree or two.
Paul