Undeserving & Lucky Promotion to Manager Position?

Have you ever been in a position where you accepted a promotion to a Manager position due to lucky circumstances like your boss leaving?

Well, it happened to me...I don't feel like I deserve it nor do I have the necessary experience yet...Never imagine it to be this early into my career as I was expecting it in a couple of years...I was only recently promoted to Senior 4 months ago too.

I don't have the designation typically required for this role, but I am at the final stages of it. I have been with the company for a few years and my boss believes I do have the technical skills to do the job and my team supports me. I'm pretty pessimistic about my survival in this position, as it will bring lots of scrutiny (internal & external), stress, pressure, and some overtime.

I won't specify the field nor department as I want to remain anonymous.

What are your thoughts or similar experience and how it turned out in the end?