T-SQL - How to rollback or commit a transaction in Microsoft SQL Server

declare @QuantitySelected as char
    set @QuantitySelected = 2

    declare @sqlHeader as varchar(1000)
    declare @sqlTotals as varchar(1000)
    declare @sqlLine as varchar(1000)

    select @sqlHeader = 'Insert into tblKP_EstimateHeader '
    select @sqlHeader = @sqlHeader + '(CompanyID,CompanyName,ProjectName,EstimateID,EstimateHeader,QuoteDate,ValidUntil,RFQNum,Revision,Contact,Status,NumConfigurations) '
    select @sqlHeader = @sqlHeader + ' select CompanyID,CompanyName,ProjectName,EstimateID,EstimateHeader,QuoteDate,ValidUntil,RFQNum,Revision,Contact,Status,NumConfigurations '
    select @sqlHeader = @sqlHeader +  'from V_EW_Estimate_Header where EstimateID = 2203'



    select @sqlTotals = 'Insert into tblKP_Estimate_Configuration_Totals '
    select @sqlTotals = @sqlTotals + '(ConfigRecId,RecId,SellQty,ConfigNum,ConfigDesc,SortOrder,OptionsInMainPrice,MarkupPctQty,'
    select @sqlTotals = @sqlTotals + ' SellPriceQty,RubberStamp,OptPriceQty,StatusRecid,LastUpdate_Date,LastUpdate_User,TotalCost,QuantityBracketSelected)'
    select @sqlTotals = @sqlTotals + ' select ConfigRecId,RecId,SellQty' + @QuantitySelected + ',ConfigNum,ConfigDesc,SortOrder,OptionsInMainPrice'
    select @sqlTotals = @sqlTotals + ' ,MarkupPctQty' + @QuantitySelected + ',SellPriceQty' + @QuantitySelected + ',RubberStamp,OptPriceQty' + @QuantitySelected + ',StatusRecid,LastUpdate_Date,LastUpdate_User,TotalCost' + @QuantitySelected + ',' + @QuantitySelected
    select @sqlTotals = @sqlTotals + ' from v_EW_Estimate_Configuration_Totals where ConfigRecId = -3'


    select @sqlLine = 'Insert into tblKP_Estimate_Configuration_Lines'
    select @sqlLine = @sqlLine + '(MstrRfqRecId,RfqRecId,RfqLineRecId,CompanyId,VendorQuoteNum,LineGrp,LineNum,StatusRecId,'
    select @sqlLine = @sqlLine + ' LineDesc,LineSize,LineMatl,LineDeco,LineFinish,CopyFromRecId,PerPieceCost,IsOptional,'
    select @sqlLine = @sqlLine + ' CopyToNewRev,RecId,UnitPrice,LineQty,LinePrice,CustOrVend,SellQty1,RfqNum,ConfigLineIsOptional,ConfigLinePerPieceCost,ConfigLineRecid,SellPrice,SaleQty)'
    select @sqlLine = @sqlLine + ' select distinct MstrRfqRecId,RfqRecId,RfqLineRecId,CompanyId,VendorQuoteNum,LineGrp,LineNum,'
    select @sqlLine = @sqlLine + ' StatusRecId,LineDesc,LineSize,LineMatl,LineDeco,LineFinish,CopyFromRecId,PerPieceCost,IsOptional,'
    select @sqlLine = @sqlLine + ' CopyToNewRev,RecId,UnitPrice' + @QuantitySelected + ',LineQty' + @QuantitySelected + ', isnull(LinePrice' + @QuantitySelected + ', 0.0000),CustOrVend,SellQty' + @QuantitySelected + ',RfqNum,ConfigLineIsOptional,ConfigLinePerPieceCost,ConfigLineRecid,SellPrice' + @QuantitySelected + ',SaleQty' + @QuantitySelected
    select @sqlLine = @sqlLine + ' from v_EW_EstimateLine  where rfqlinerecid in (select RfqLineRecID from kp_tblVendorRfqConfigLine where ConfigRecID = -3) '

BEGIN TRY
    BEGIN TRANSACTION 
        exec( @sqlHeader)
        exec(@sqlTotals)
        exec(@sqlLine)
    COMMIT
END TRY
BEGIN CATCH

    IF @@TRANCOUNT > 0
        ROLLBACK
END CATCH