Qingdao, I would have a think about what specific areas make you feel underqualified or out of your depth (as Purple suggested). Write these down. Then have a think about how you could go about addressing these, eg: is there a course I can do? is there someone in the organisation that can mentor me? could internal communications be improved so that my team see me as the leader?
Only when you've identified the problems and some possible solutions should you ask your manager to schedule a review meeting with you. Then, together, you can put a plan in place, so that you are equipped to grow into the role. Your manager has a responsibility to help your transition and to support you along the way, but it is important, in looking for help from him/her, that you have given some thought to solutions in advance.
Very best of luck to you.