Is a chin reduction dangerous? I have a long chin and I think a chin reduction would help, but i’m worried about letting the doctor actually take out bone. Could that be dangerous? And what if he takes out too much?

Chin reduction. It is not dangerous if done by an expert. I would stay away from shaving the chin. .
It . It can be if not done properly - in addition one needs to consider your occlusion (how your teeth fit together) removing jaw bone - can weaken it and make you susceptible to a fracture when you get older.
Surgical risks. All surgeries have risk and certainly removal of bone has risks involved. You mention real risks and the best bet is to find a surgeon with a large amount of experience performing this procedure. As a plastic surgeon i was trained in this procedure yet do not perform it. Some surgeons perform it frequently. Best to find someone who does this often to discuss risks and goals. Best of luck!