If the scan is too magenta, the film is too green. This can come from a variety of effects including fog, improper development and a host of other things. Since I have no idea what your workflow is, I cannot judge but if it is truly magenta then the problem is in the yellow and cyan layers or in the magenta layer.

Is the entire film greenish? Or, is just the image area greenish? Or, is there no cast to the negative in any way, but it scans magenta? This might help evaluate the problem.