OP stated they were on a two lane road and had their right hand turn signal on. Even if they were slightly across the white/yellow line, the majority of their vehicle combination was still in the lane. That would mean the following driver had to move to the right OUT of the lane onto the shoulder in order to try and pass.
IMHO the following driver was in the wrong. However good defensive driving skills of the OP's vehicle by closely watching their right side rear view mirror could have probably prevented any contact.
In some states, if a vehicle is completely stopped on a two lane road waiting to make a left hand turn, it is legal for a following vehicle to SLOWLY pass on the right even if it means using the shoulder.
