Format Decimal

I want to format a number, a decimal, with 2 figures afther the "," but all I get is zeroes behind it. It works if I replace  "cart.GetTotalWeight(cartId)" by 12.12 for example, 12,12 does not work... It driving me crazy

 

dim cart = New ShoppingCartDB()
TotalweightLbl.Text = string.Format("{0:n}", cart.GetTotalWeight(cartId))

the stored procedure...


CREATE Procedure CMRC_ShoppingCartTotalweigh
    (
        @CartID    nvarchar (50),
        @Totalweight  decimal (5,2) OUTPUT
      
    )
    AS

    SELECT
        @Totalweight = SUM(Products.Unitweight * ShoppingCart.Quantity)
       
    FROM
        ShoppingCart,
        Products

    WHERE
        ShoppingCart.CartID = @CartID
      AND
        Products.ProductID = ShoppingCart.ProductID
GO

the function....

Public Function GetTotalweight (ByVal cartID As String) As Decimal

            ' Create Instance of Connection and Command Object
            Dim myConnection As SqlConnection = New SqlConnection ConfigurationSettings.AppSettings("ConnectionString"))
            Dim myCommand As SqlCommand = New SqlCommand("CMRC_ShoppingCartTotalweigh", myConnection)

            ' Mark the Command as a SPROC
            myCommand.CommandType = CommandType.StoredProcedure

            ' Add Parameters to SPROC
            Dim parameterCartID As SqlParameter = New SqlParameter("@CartID", SqlDbType.NVarChar, 50)
            parameterCartID.Value = cartID
            myCommand.Parameters.Add(parameterCartID)


            Dim parameterTotalweight As SqlParameter = New SqlParameter("@Totalweight", SqlDbType.decimal, )
            parameterTotalweight.Direction = ParameterDirection.Output
            myCommand.Parameters.Add(parameterTotalweight)

            ' Open the connection and execute the Command
            myConnection.Open()
            myCommand.ExecuteNonQuery()
            myConnection.Close()

            ' Return the Total


             If parameterTotalweight.Value.ToString() <> "" Then
                Return parameterTotalweight.Value
            Else
                Return 0
            End If

        End Function