[rohrmann]

What you have is nominal 3” ABS pipe that is 3 1/2” outside diameter. You may have the part of the flange fitting still glued to the outside of the 3” pipe nipple which would give you about the diameter dimension you are seeing. You will need to somehow remove that part from the nipple in order to glue a new flange fitting to the nipple so you can mount a new drain valve to it.