Is there a way to have the selected area rotate below 90 degrees? Im trying to add water to my game using the region select tool but the rotation of the selected area only rotates 90 degrees.
Nope.
Terrain Voxels are not like Parts so they can only be rotated by 90 degree increments.
Another way is to make a short angled section of water/shoreline, select that region, and resize it to the size you want your entire lake or river shore to be.