Q: Set screen lock by accident. Don't know password.How do I remove screen lock?

Try very hard to remember the password.  If the instructions in the iPod: How to use the Screen Lock does not work, read the iPod Manuals

In the future if you are going to use passwords, use one that you will never forget & no one else can figure out.  Keep the password in a safe place off and online (use a password manager).