35 yrs old male, found multiple lung nodules 2 are 4mm should i worry, pulmonary doctor says i should not worry?

Agree: Lung nodules that small, in someone your age are probably nothing to worry about. I agree that a follow up scan is necessary to ensure that they do not enlarge.

To worry or not.: In this context, there's a difference between "don't worry, it's not cancer" and "don't worry, there's nothing wrong." While I wouldn't think first about cancer with your description, I would be curious that those nodules would be there for some reason. While I may not be inclined to worry right now, I wouldn't ignore them in the long run.