You have 13 columns in the first select and 14 in the second select in the union.
SELECT 'TOTALS' serialnumber,
' ' firstname,
' ' keyname,
' ' country,
' ' classof,
' ' giftaid,
' ' mailingsegment,
' ' [Payment Date],
SUM(bd.Paymentamount) Amount,
'' total,
' ' destinationnotes,
' , ' paymenttype,
' ',
100000 Row
Look for second to last column without an alias.