Try these actions one-at-the-time. (you could do it all at once, but then you won't know which one did the trick...or which one make it worse)

Increase the incidence of the wing relative to the float. 4-5 degrees should work. Airplane nose up/float nose down.

Scoot the floats forward a half inch.

If you have a computer radio and dual aileron servos, droop the flaperons 15 degrees.

Use full up elevator for the first ten feet of your run. Then neutralize the elevator and let the airplane accelerate. Gentle back pressure once the plane has reached takeoff speed should get it airborne. Conversely, Holding a bunch of up just makes the tail of the floats dig in and act as hydro-brakes. You should not, and you should not need to, rotate so far that the tail of the float touches the water.

Be sure the floats are parallel when looking from the top. No toe-in or toe-out.

Water rudder(s)? Make sure they don't stick down from the transom any farther than the height of the step.

I'm no fan of GeeBee floats, but you >SHOULD< be able to get airborne. If it will go fast enough to fly, it should fly. Proper floats DO help. There are a lot of foam float vendors linked on the Florida Float Flyers website.