Two login accounts, admin account password unable to login
First, setting up separate admin and standard accounts was NOT a mistake. It is, in fact, a Good Idea™.

When you need to authenticate (for example, to unlock a padlock), you need to enter both your admin name and your admin password. If you're in your admin account, the name will be filled in for you. If you're in your standard account, both the name and password fields will be blank, and you need to enter them both. Be sure to enter the admin's name and the admin's password.