Did I delete my user account?

I got a new computer with Windows 10 on it and saw it gave me a username that is half of what I want it to be. I went to start>netplwiz and changed the name to what it was on my old computer.
It changed the name. Great. Then I got the following error when I went to the start menu "no mapping between account names and Security ID's was done."

When I go to find the user, it's gone completely. There is no administrator left and it shows no additional accounts so I'm thinking it somehow deleted it completely? What should I do? I did not back it up and am afraid to restart the system.

Berton said:

The User name on one of my computers got only the first 5 characters from my E-Mail address used when installing and using the Microsoft Account.

Okay.

Hopefully, you still have administrator access. What you need to do is create a local account with the username that you want:
Add Local Account or Microsoft Account in Windows 10

Make sure to change it to an administrator:
Change Account Type in Windows 10

If you have lost administrator access, you can regain it by enabling the built-in administrator account (option 5):
Enable or Disable Elevated Administrator account in Windows 10