If you have the bow limbs straight and the shape of the notch rounded into a perfect tear drop, you do not need any shoulders, and the string will not wander off track. i would carefully reshape the notch and check it for dead center.
I've had problems with this myself a lot in the past until i really started paying close attention to the shape of the tip notches. Brutha Sixby hammered that one into me.....
using the shoulders of the limb to hold your limb straight does nothing for the way the limb tracks while drawing it..... learned that one the hard way, and i still battle with it from time to time.