Prop question on a 20'

[Sceptre20]

I have a 20' Sceptre that is powered by a Yamaha f100 four stroke.I am running a four blade prop on it and find that the boat is unresponsive at slow speeds,it requires constant adjustments at the helm to stay on course and when docking or loading onto the trailer it is very slow to respond,the steering is a brand new baystar hydraulic unit and seems very tight.I was wondering if the four bladed prop could have anything to do with the problem and if others had experienced the same problem.any input would be helpful.