When in doubt, follow the instructions. Sorry mate, but if you had followed the instructions, you would probably not be in the pickle that you are in. The whole program is more than 150gB, and it will need to apply multiple updates to bring it up to date. At least during the early days there are quite frequent, often large, updates flying out of Asobo's shop.
Head over to https://www.flightsimulator.com/, which is the official MSFS 2020 support site, and repeat your woes there. I'm sure that some kind soul will come to your rescue.
BTW, does the disk version come with a manual? And is it any good? Us poor "downloaders" got no documentation at all, so a lot of us headed over to https://sofly.io/flight-simulator-guide/ and have a look at their (paid) offering. It covers most of what you will need once you get the sim up and running.
Good luck