My first hull was perfect to scale, not one defect, I was all smiles until I put that bad boy in the water.
Did you consider everything into your calculations? Such as....the weight of the cage, the weight of the motor, the CG of the boat, the balance point, the weight of the grass rake, rudder proportion, the actaul boat weight, etc. If your gonna be precise, then you have to include everything. If you do not scale this down from the full size also...your not getting a "perfect" scale down...probably why you were disappointed.