May be you have solved this issue, but here is my answer:

I had similar problems, getting double entries, error messages and all trying to insert all the given names in one go in the created table. It looks like you cannot enter multiple records all at once.

When I entered and executed the statements for each record before adding the next record, it worked fine. (Either back page the browser and enter the statements for the next record in the same box after clearing the box or enter in the blank box that appears after it interprets the first record's statements.)

I agree that the lesson should be more clear. But searching for the answer on google, I got the idea that inserting multiple records into a table with one set of statements is only possible in the latest SQL interpreters. Am I right?