SSRS SQL PIVOT Multiple Rows Required for Result

SELECT *
FROM
(
	SELECT
	SalesLineItems.[Item Class Code],
	  SalesLineItems.[Item Number]
	  ,SalesLineItems.[Customer Name]
	  ,(SELECT CASE ISNULL ([Tax Exempt 1 from Customer Master], '')
           WHEN ''
           THEN NULL
           ELSE CAST ([Tax Exempt 1 from Customer Master] AS DECIMAL (10,2))
         END) as [Dispenser Cost]
	  ,SalesLineItems.[GL Posting Date]
	  ,SalesLineItems.[SOP Number]
	  ,CASE WHEN LEFT (SalesLineItems.[SOP Number],2)='CR' THEN sum(SalesLineItems.[Extended Price]*-1) ELSE sum(SalesLineItems.[Extended Price])END as [Extended Price]
	  ,datename(month,SalesLineItems.[GL Posting Date]) as FMonth
	  ,datename(year,SalesLineItems.[GL Posting Date]) as FYear
	  ,CASE WHEN LEFT (SalesLineItems.[SOP Number],2)='CR' THEN sum(SalesLineItems.[QTY]*-1) ELSE sum(SalesLineItems.[QTY])END as [QTY]
	  
	  
	  FROM
	  SalesLineItems
	  
	  WHERE
	  SalesLineItems.[SOP Type] IN ('Invoice','Return')
	  AND SalesLineItems.[Void Status] <> 'Voided'
	  AND SalesLineItems.[Document Status] = N'Posted'
	  AND SalesLineItems.[Extended Price] != 0
	  AND SalesLineItems.[Item Class Code] IN (@ItemClassID)
	AND datename(year,SalesLineItems.[GL Posting Date]) = @FYear
	GROUP BY 
	  SalesLineItems.[Item Class Code]
	  ,SalesLineItems.[Item Number]
	  ,SalesLineItems.[Customer Name]
	  ,SalesLineItems.[Tax Exempt 1 from Customer Master]
	  ,SalesLineItems.[GL Posting Date]
	  ,SalesLineItems.[SOP Number]
	  ) as DerivedTable

PIVOT (sum([Extended Price]) for FMonth in ([January],[February],[March],[April],[May],[June],[July],[August],[September],[October],[November],[December]))
AS NEWMONTH