Welcome to the Forum.
Perhaps what you did was click that Rename this PC
button in Start > Settings > System > About
but that will not alter your User Profile's Username.
I posted an Article the other day to help Users who want to change their current Username.
It's a little tricky to do, but if you follow the instructions given in the order given, you should not have any trouble achieving your goal. As a precaution though, before starting you could create a System Restore Point to back up the Registry, and if you want a System Image to fully backup everything including files etcetera.
The Article can be read here: