Hello,
Thank you for the update on the issue.
You might be missing some steps mentioned above. I have already reproduced the scenario at my end and was able to create default administrator account.
If you were unable to create default administrator account from the steps mentioned above you may try the steps provided below.
Firstly, you need to open the command prompt with administrator rights. Just press the
Windows key to open the metro interface and then type command prompt in the search box
Next, right-click on command prompt and Run it as administrator.

Copy this code net user administrator /active:yes and paste it in the command prompt. Then, press
Enter to enable your built-in administrator account.

Once you’re done, you can access your built-in administrator account by logging off your current account anytime.

Do take note that you can’t change the name of the built-in administrator account; it will always stay as Administrator.
Hope this would help. Do keep us updated about the issue.