Job promotion that I can't handle, what should I do?

Anonymous
I've recently have been promoted at my work. I work for a Toyota dealership, my previous position was used sales manager, I only took care of the sales for the used cars. While I was at this position, I managed to make the used cars department larger by implementing a strategy that I discussed with the owner before I was hired. The strategy worked and caused a 70% increase in used cars sales within 2 years.The owner was impressed, So, he promoted me as the General Manager, my duties are to control the Used sales, New car sales and the service department. The dealership holds 640 cars, so I assume you can image the work that I have taken on. I've experienced a high pay increase as well :). But the tasks that I have to do are challenging me, I feel very pressured and I am scared of failing. Just thinking about failing, makes me go crazy, I have a very good relationship with the owner. The owner repeatedly mentioned that I am operating a business that is worth 80 million dollars, which puts even more pressure on me. I've thought many times to confront the owner and inform him that I am not ready for this position, but I am not sure if that is a good idea. So What I am asking GAG users is, what would you do if you were in my position? What did you do in the past when you have taken tasks that you feel unsure of accomplishing?

Thanks in advance.
Job promotion that I can't handle, what should I do?
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