it never existed and while it is fairly easy to reset the account password, that does not reset the Keychain Password.
Here is what I would suggest.
As you have not had this machine for very long, it seems, you probably do not have a bunch of stuff that accrued on that machine.
Launch Terminal from the Applications/Utilities folder
Copy and paste the following: rm /var/db/.AppleSetupDone
Once done, close all the open windows and reboot.
The MBP will now boot and it will not find that directory and file so it will assume that this is a first time out of the box boot-up
Now go through the setup process and create yourself an Admin account and give yourself a Password.
Continue to use that account and all will be well.
Alternatively, if you have a bunch of stuff that you need
Make a folder inside the Shared Folder, Hard Drive/Users/Shared, and make folders inside there called Documents, Music, Photos, Movies.
Copy the contents of the corresponding folders from your user drive into the newly created folders.
Repeat until all the stuff has been copied.
Now run that Terminal command as shown above and create the new Admin account.
Once done, copy the Contents of the folders in the Shared Folder back into the corresponding folders inside the newly created User account.
(Copying stuff into the Shared Folder ensures that there will not be a permissions problem when you try to use whatever file is inside there)
Let us know how you get on
P