Is your "form" a portal or a layout that includes a portal?
Simply inputting data into a FileMaker layout won't, under normal circumstances, create any new records let alone two so we need a more detailed description of what you have set up and what you are seeing that leads you to conclude that you have two new records.
It is a layout that does indeed include a portal - five actually.
When I enter a new record, I input directly into the field 'Company_Name' that also drops down to reveal other companies on the database, which can be selected, and then proceed to fill in data on the other fields.
When I create a new record, a blank duplicate is also created under the name of the original record, and these seem to be interlinked as deleting one deletes both.
A "blank duplicate" in what? The row of a portal? This can be normal behavior for portals configured to add new portal records through data entry in the portal. The blank row is the "add row" that appears for adding the next new record in the portal. This row will or will not be visible in a portal depending on whether "allow creation of records via this relationship" is or is not enabled in the relationship on which that portal is based.
But I can't tell from what you have described if this is what you see or not.
Thanks for that.... definitely a portal issue. All the portals are empty except for one portal that lists staff members drawn from a separate contact table. There was only one contact assigned to the company I was having problems with and there was a blank row under that entry so I will investigate the allow create/delete options in the relationship and see if that works.
Thanks for your help!
Note that disabling this option changes what you can do with your portal. It may be the better option, but you will lose the ability to just start entering text into that blank "add row" as a way to add new records in the portal's table. (Many developers put a button on the layout that creates new portal records instead of this add row.)