Transact SQL :: Add A Grand Total To Pivot Output?

I have a SP that will generate a pivot output. I want to add a grand total at the end row to sum up the counts for each column.

the SP is as below :

/* COLUMN HEADERS*/
DECLARE
@columnHeaders NVARCHAR (MAX)
SELECT
@columnHeaders  =  COALESCE ( (@columnHeaders)  + ',[' + [Date] + ']', '[' + [Date] + ']')

[code]....

I am getting the below error:

Invalid column name 'Grand Total'.

Msg 205, Level 16, State 1, Line 16

All queries combined using a UNION, INTERSECT or EXCEPT operator must have an equal number of expressions in their target lists.