The hardest part about the chin is the "Round" part. If you break the chin up into 3 areas, you might have better luck. Light pressure is definitely key. Under the lip is one area that is pretty flat so it is easier to maintain an angle similar to your cheek as are the two sides of the chin which also take well to the what I call a flat stroke and it is easier there to maintain a more vertical angle of attack. The hard part about the "Round" is that it takes practice rolling the razor around that part of the chin and maintaining your cutting angle. Only practice will work in the long run.

The neck can be problematic because the hair for most of us grows in funny directions and the tendency is to use too much pressure and too many passes trying to shave there. Experiment with stretching the skin toward the sides of the neck and see if that helps with lighter pressure and only a couple passes.

Have fun.