Accidentally converted Admin account to managed

I bought a new iMac and used the Time Machine backup to transfer all the files from the old iMac (which just had a single admin user). On the new iMac, I wanted to set up Parental Controls so I converted the single admin user to a managed user. When I went to make changes to the Parental Controls later on to whitelist some sites that were being flagged incorrectly, I tried to log in and make changes but it said my admin password was wrong. Since I didn't change the password, and it still works on the old iMac, I'm not sure what the issue is. I tried restoring from the backup again but that didn't fix it. Any ideas where to go next? Thanks.