At first he will take off to the back of the cage. If he gets upset and won't come back to your hand, wait a few days before you try to rub him again. The idea is too gain trust, not loose it. I do have a few chins. The moment you touch them, they shake and rub their heads.
All chinchillas are different.
Some may follow this example perfectly, and others will be painfully slow. Some may love petting from the start. I wrote this to give some ideas as to how gaining trust might be done. What works for me may not work for you. When it comes to you and your animal, you will have to find what is right for you.