I'm asked to calculate a stone being dropped from rest to hit the water it takes 2.7s I found the final velocity to be 26.46m/s
No, because you are assuming that the stone hits the water at the same speed in both cases. If you fire a rifle bullet into the water then you will see that that cannot be true. (Good general principle in thought experiments: before getting seduced by numbers and formulae, make a picture in your mind of an extreme case and see how the concepts fit).
The stone will hit the water at a speed $2.3g$ greater at that with which you threw it. The average speed of the stone will therefore be $1.15g$ plus your throw. The distance the stone fell will therefore be $2.3$ times that.
Since, from dropping the stone and it taking $2.7$ seconds you know what the distance to the water is, you can work backwards and get the speed of the throw.