Before you make any changes, try a little up elevator trim, while on step, which will drop the rear of the floats a little. The problem you are having is caused from too much float ahead of the step in the water. You need to raise the front of the floats and lower the rear. This will allow the rear of the floats to slightly drag in the water which will stabilize the situation. While on step, you want just the step and the rear of the floats in the water. If the little bit of up trim causes the situation to settle down, but the plane tends to take off too soon, then you will need to make some changes to the float struts.
Hope this helps........Seaplane