If you duplicate the same field while in layout mode, this won't work for you. The fields all reference the same location in the same record of the same table and thus store only one instance of the information entered. You could open manage | database | fields, define additional fields and then use the field tool to add them to your layout, but I don't recommend it. Think of what happens once you have used all your fields to record a note being sent. To record more requires making design changes to both the table and the layout.
Instead, you should look up "portal" in FileMaker help. You should create a related table for notes with each record having a date and text field as well as a "match" field that links records in this new table to a serial number field in your original table.
Set this up right and you can put a portal to this new table on your layout and you can log an unlimited number of such events for any given customer simply by entering the data in a blank row in this portal.
Read the help page on portals. Will have to dig deeper to try and understand related tables, match fields, and serial number fields.
The last paragraph describes exactly what I want to do - a table where I can log an unlimited number of events (thank you card sends) into a blank row - like in Excel. Sounds like I need to wrap my brain around being relational in a database.