Flash Fill in Office 2016

I'm using Office 2016 on a Dell Inspirion computer with a Core 7 processor, 16 GB RAM and Windows 10 Enterprise.  When I go to use Flash Fill, I keep getting a message stating that Excel can't find a pattern to use Flash Fill.  For example, in trying to create user email addresses, I have a first name and last name fields,  I'm entering the first initial and last name for each user and adding @email.com.  For example, Joanne Bennett would have and email address of jbennett@email.com.  After entering each user, I use the down arrow to go to the next user.  After the 2nd user, I press the ENTER key, then select Flash Fill from the Data ribbon.  I keep getting a message that Excel cannot determine a pattern.

Flash Fill is enabled under options.  It does not matter if I press the down arrow or enter key after2, 3, or 4 entries, the result is the same.  Anyone got any suggestions?  Answers?