How to Get sum of first record amount and second amount is in Total Amount using Sql server STored Procedure

Get sum of first record amount and second amount is in  Total Amount
In this table i want to insert value fot sum of first and second temp_id is total_sum of second temp_id and than after repeat loop for it.
This is Table Script.

 USE [temp]
GO
/****** Object: Table [dbo].[TblTest] ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
SET ANSI_PADDING ON
GO
CREATE TABLE [dbo].[TblTest](
[temp_id] [int] IDENTITY(1,1) NOT NULL,
[temp_name] [varchar](50) NULL,
[sum] [int] NULL,
[Total_sum] [int] NULL
) ON [PRIMARY]

GO
SET ANSI_PADDING OFF

Stored Procedure :-

Alter procedure ProcTestGet
@temp_name varchar(50),
@sum int
AS
Declare @Tmp_id As int
Declare @total_sum As int
Declare @sum1 As int
select @Tmp_id = @@identity
If @Tmp_id = 0
Begin
set @total_sum =Null
insert into TblTest(temp_name,sum,total_sum) VALUES(@temp_name,@sum,@total_sum)
End
else
begin
select @total_sum = total_sum from TblTest where temp_id = @@identity
if @total_sum = NULL
begin
select @sum1= sum from TblTest where temp_id = @@identity
declare @totalsum int
set @totalsum = @sum1 + @sum
insert into TblTest(temp_name,sum,total_sum) VALUES(@temp_name,@sum,@totalsum)
end
else
begin
select @total_sum = total_sum from TblTest where temp_id = @@identity
declare @totalsum1 int
set @totalsum1 = @total_sum + @sum
insert into TblTest(temp_name,sum,total_sum) VALUES(@temp_name,@sum,@totalsum1)
end
select @@identity
End

 exec ProcTestGet  '1',600    -- Execeute Stored Procedure
 select * from TblTest           -- Run query to see result