Stored Procedure Concurrency failure issue with Inserting Primary key value - sql

Question

I am executing stored procedure with multiple request at same time then it fails and i am getting below error.
"Violation of PRIMARY KEY constraint 'PK_catalogs_mstr'. Cannot insert > duplicate key in object 'dbo.catalogs_mstr'. The duplicate key value is > (1).\r\nThe statement has been terminated."
My Table has Catalog_Code column as Primary key with out Auto increment. I am trying to generate value for this column with in stored procedure.
CREATE PROCEDURE [dbo].[usp_CreateCatalogDefination]
#AccountId INT,
#UserId INT,
#CatalogName NVARCHAR(100),
#DataSourceTypeId SMALLINT,
#AttributeGroupId SMALLINT,
#ReferenceCatalogCode INT,
#ImageName NVARCHAR (100),
#ImageFile NVARCHAR (100),
#ImagePath NVARCHAR (100),
#Result int OUTPUT
AS
BEGIN
SET NOCOUNT ON
/* Declaration Block */
DECLARE #ErrorMessage NVARCHAR(4000)
DECLARE #ErrorSeverity INT
DECLARE #ErrorState INT
DECLARE #ValidReferenceCatalogCode INT
BEGIN TRY
BEGIN TRANSACTION
IF EXISTS(SELECT id from accounts_mstr WHERE id=#AccountId AND account_type_id =2) /* Account should be of Seller Type */
BEGIN
IF EXISTS(SELECT id from users_mstr WHERE id=#UserId) /* Check for Valid User Id */
BEGIN
/* Generate Catalog Code */
DECLARE #CatalogCode INT
SET #CatalogCode = (SELECT TOP 1 catalog_code FROM catalogs_mstr Order By catalog_code desc)
IF(#CatalogCode IS NULL)
BEGIN
SET #CatalogCode = 1
END
ELSE
BEGIN
SET #CatalogCode = #CatalogCode + 1
END
IF EXISTS(SELECT id from attribute_groups WHERE id=#AttributeGroupId) /* Check for attribute group */
BEGIN
INSERT INTO [dbo].[catalogs_mstr](
[catalog_code],
[seller_account_id],
[user_id],
[catalog_name],
[datasource_type_id],
[attribute_group_id],
[image_name],
[image_file],
[image_path]
)
VALUES (
#CatalogCode,
#AccountId,
#UserId,
LTRIM(RTRIM(#CatalogName)),
#DataSourceTypeId,
#AttributeGroupId,
LTRIM(RTRIM(#ImageName)),
LTRIM(RTRIM(#ImageFile)),
LTRIM(RTRIM(#ImagePath))
)
COMMIT TRANSACTION
SET #Result=1 /* Success */
RETURN #Result
END
ELSE
BEGIN
ROLLBACK TRANSACTION
SET #Result=2 /* Invalid Attribute Group Id */
RETURN #Result
END
END
ELSE
BEGIN
ROLLBACK TRANSACTION
SET #Result=4 /* Invalid User Id */
RETURN #Result
END
END
ELSE
BEGIN
ROLLBACK TRANSACTION
SET #Result=5 /* Invalid Seller Account Id */
RETURN #Result
END
END TRY
BEGIN CATCH
--USE CATCH BLOCK FOR RAISING ERROR TO APPLICATION END
IF ##TRANCOUNT > 0
ROLLBACK TRANSACTION
SELECT #ErrorMessage = 'Error : ' + HOST_NAME() + ' : ' + OBJECT_NAME(##PROCID) + ' : '
+ ERROR_MESSAGE(),
#ErrorSeverity = ERROR_SEVERITY(),
#ErrorState = ERROR_STATE();
RAISERROR (
#ErrorMessage,
#ErrorSeverity,
#ErrorState
);
RETURN
END CATCH
SET NOCOUNT OFF
END