sp_executesql in procedure with separate query,parameter

CREATE PROCEDURE Myproc-- 'pabitra','@parm1OUT',''
    @parm varchar(10),
    @parm1OUT varchar(30) OUTPUT,
    @parm2OUT varchar(30) OUTPUT
    AS
      SELECT @parm1OUT='parm 1' + @parm
     SELECT @parm2OUT='parm 2' + @parm
GO
DECLARE @SQLString NVARCHAR(500)
DECLARE @ParmDefinition NVARCHAR(500)
DECLARE @parmIN VARCHAR(10)
DECLARE @parmRET1 VARCHAR(30)
DECLARE @parmRET2 VARCHAR(30)
SET @parmIN=' returned'
SET @SQLString=N'EXEC Myproc @parm,
                             @parm1OUT OUTPUT, @parm2OUT OUTPUT'
SET @ParmDefinition=N'@parm varchar(10),
                      @parm1OUT varchar(30) OUTPUT,
                      @parm2OUT varchar(30) OUTPUT'

EXECUTE sp_executesql
    @SQLString,
    @ParmDefinition,
    @parm=@parmIN,
    @parm1OUT=@parmRET1 OUTPUT,@parm2OUT=@parmRET2 OUTPUT

SELECT @parmRET1 AS "parameter 1", @parmRET2 AS "parameter 2"
go
drop procedure Myproc