You'll be OK. Although there are "rules" ( Punctuation markes are to mimic when Dr. Evil said "Lasers") , the step placement is not vastly critical and having it too far back will only make the plane want to run truer on takeoff and possibly be sluggish on the elevator. When you land ( water?) it will probably rock forward and kill all the lift, But I can't imagine the plane nosing over with all that buoyancy in front of the prop.

Still, I think back to the post where the suggestion was offered that your floats are too long.

Ideally (there's the "rule") the step of the float should be under a point corresponding to 40% of the wing chord.
Then the Nose of the float should be about 20% of the prop diameter in front of the prop.
And the overall length of the float is 75-80% of the distance from the prop washer to the rudder hinge line. That SHOULD be double the distance of the nose to the step. Betcha your floats are bigger than that.

I have been fantasizing about building another Mud Duck for floats. I had one of the originals from the MA plans, and I LOVED it. That one was balsa and ply, and flew with authority on a .25 HB. I tried a Crikit, and it wouldn't fly at all. I think I'd like to scale up a Mud Duck to about 70" WS, and use a .70 4-stroke. Whatever happened to the designer, Tom Chipley, anyhow??