Data Grid Formatting

What's wrong? I have looked over this bit of code for days. Everything looks right, but my data grid still doesn't get formatted.

Code:

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Dim conn As SqlConnection = New SqlConnection("Data Source=ADVTIS-DB;Initial Catalog=RainMaker;User ID=sa;")
        Dim dataAdapter As SqlDataAdapter = New SqlDataAdapter("Select ID, Description, MfgNum, ProductSize from AT_Product", conn)
        Dim dt As DataTable = New DataTable()
        dataAdapter.Fill(dt)

        DataGrid1.DataSource = dt

        Dim tableStyle As New DataGridTableStyle()
        tableStyle.MappingName = "AT_Product"

        'MfgNum
        Dim column As New DataGridTextBoxColumn()
        column.MappingName = "MfgNum"
        column.HeaderText = "Mfg #"
        column.Width = 70
        tableStyle.GridColumnStyles.Add(column)

        'Item Description
        column = New DataGridTextBoxColumn()
        column.MappingName = "Description"
        column.HeaderText = "Description"
        column.Width = 140
        tableStyle.GridColumnStyles.Add(column)

        'Size
        column = New DataGridTextBoxColumn()
        column.MappingName = "ProductSize"
        column.HeaderText = "Size"
        column.Width = 70
        tableStyle.GridColumnStyles.Add(column)

        Me.DataGrid1.TableStyles.Add(tableStyle)

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