OK, now you're hooked! It's possible that the nerves were the cause of the gyrations before takeoff, and that you gave it too much throttle too quickly, it started to torque on you and you over corrected. A plane that's not on wheels or doesn't have a water rudder can do that as there's not much frictional contact with the surface (water) as there is when on wheels and ground. This could be much better the next flight without any mods to the plane. I have Ernst water rudders on my floats, and they are good, but as was mentioned, water rudders are out of the water when the plane is on step.

As to the nervousness, I have found that I'm always more nervous when flying off water than when off the ground - especially as the season starts.

Good luck.