It is normal to wear the outside shoulders when tracking a stock M3. The camber we run stock isn't enough for tracking the stock tires. Plus the PS2s, even though they have excellent grip, have very poor durability on the track. I think they wouldn't last for more than 3 track days and they are hugely expensive.
However, the stock camber is good for any kind of regular non-track driving. If you plan to track the car often I think it is best to get a set of dedicated wheels & tires for the track.