Seaplane is right, but if reducing the incidence doesn't do it, consider this; Your trainer has a lot of downthrust built in. When you use full throttle for take off, the downthrust forces the front of the floats deeper into the water. The resulting high pressure on the front of the floats causes the airplane to dart off to one side or the other.

The solution is to move the floats forward. Put the step 1" in front of the CG. I've done it and it helps.

Jim