I'm having a great deal of difficulty with equating my SQL workflow experience to how FileMaker Pro does things. I just found a data import problem with a table that was created from an Excel file, all of the record fields were not imported. I'd like to know what's the FileMaker Pro equivalent to an SQL Append query?
The closest equivalent would be what you just described--using import records to import your data as this will append new records to the existing table unless you select one of the options for updating records instead of adding new.
You are welcome to describe what you attempted in more detail if you'd like some assistance in getting all of those excel columns into your table.