Should I Use A Loop?

I have the following stored procedure which enters items bought by the usr in the database, inserting the user's ID, the item and the price. now every user has a unique id and every user can only buy three items; thus only three inputs must be inserted in the table, how can i do that? This is the current SP i have...

ALTER PROCEDURE [dbo].[spA_ALW_InsertIntoMLAGoods]

@MLAFormIDFINT,
@DescriptionNVARCHAR(50),
@AmountINT

AS

BEGIN
BEGIN TRY
--UPDATE MLAGoods
--SET
--MLAFormIDF=@MLAFormIDF,
--Description=@Description,
--Amount=@Amount
--WHERE MLAFormIDF = @MLAFormIDF

INSERT INTO MLAGoods
(
MLAFormIDF,
Description,
Amount
)
VALUES
(
@MLAFormIDF,
@Description,
@Amount
)
END TRY
BEGIN CATCH
SELECT ERROR_MESSAGE() AS [ERRORMSG], ERROR_SEVERITY() AS [ERRORSEV]
RETURN @@ERROR
END CATCH

END