Custom Field for a table row returned from stored procedure

I have a "lot" table with 2 columns, with one of the column is current timestamp.

I try to return another custom fields, which its calculation is based on timestamp.

(For simplicity, I include only 1 field in following example)

CREATE OR REPLACE FUNCTION create_lot(text)
  RETURNS lot AS
$BODY$DECLARE
    configurationFile ALIAS FOR $1;
    _lot lot;
BEGIN
    INSERT INTO lot(configuration_file)
    VALUES(configurationFile) RETURNING  *, extract(epoch from timestamp) as timestampex INTO _lot;
    return _lot;
END;$BODY$
  LANGUAGE 'plpgsql' VOLATILE
  COST 100;
ALTER FUNCTION create_lot(text) OWNER TO postgres;

I expect the table returns two field for a single row. 1 is configuration_file, 2nd is timestamp, 3rd is timestampex.

However, I only able to retrieve configuration_file and timestamp. How can I obtain timestampex too?

Thanks and Regards
Yan Cheng CHEOK