When creating a Google Sheet widget, you have the option to check or uncheck "Is First Column Label".
If you check it, the widget will show the data from your spreadsheet's first column. If, however, you leave it unchecked, the widget will add generic labels. (row 1, row 2, row 3...)
If you don't want the generic data, then check this field and the first column in your spreadsheet will be the first column in your Reportz Google Sheet widget.
NOTE: You cannot physically remove the first column, but can edit your first column in your source spreadsheet (leave it blank or whatever works best for you) and then check the "Is first column label" button.