Duplicate data coming into ASP.NET 2.0 GridView on DataBind

I have an ASP.NET 2.0 web form that includes a GridView control. I then have a method in the code-behind that loads the results of an SQL stored procedure into an SQLDataReader and binds it to the GridView control. In the GridView control, I've set the columns using mostly bound fields. The GridView is displaying the columns correctly, but then it goes ahead and adds extra columns, one for each column returned by the stored procedure. What's going on, and how can I get it to return only those columns that I have specifically designated inside the <Columns> tag?

Here's the ASP.NET code for the GridView:

          <asp:GridView ID="gvPlanList" ShowHeader="true" ShowFooter="false"  RowStyle-BorderStyle="none"
                    HeaderStyle-BackColor="LightBlue"
                    RowStyle-Font-Size="10px"
                    HeaderStyle-Font-Size="10px"
                    HeaderStyle-Font-Bold="true"
                    AllowPaging="false"
                    runat="server"
          >
            <Columns>
               
                    <asp:ButtonField Text="Add" CommandName="AddPlanToMyQuote" HeaderText="My Quote" HeaderStyle-BackColor="DarkBlue" HeaderStyle-ForeColor="White" />
                    <asp:BoundField DataField="Rate1" DataFormatString="{0:c}" HeaderStyle-BackColor="LightBlue" HeaderText="Employee Only" />
                    <asp:BoundField DataField="Rate2" DataFormatString="{0:c}" HeaderStyle-BackColor="LightBlue" HeaderText="Employee + Spouse" />
                    <asp:BoundField DataField="Rate3" DataFormatString="{0:c}" HeaderStyle-BackColor="LightBlue" HeaderText="Employee + Family" />
                    <asp:BoundField DataField="Rate4" DataFormatString="{0:c}" HeaderStyle-BackColor="LightBlue" HeaderText="Employee +Children" />
                    <asp:BoundField DataField="Total" DataFormatString="{0:c}" HeaderStyle-BackColor="LightBlue" HeaderText="Total Premium" />
                    <asp:BoundField DataField="Total" DataFormatString="{0:c}" HeaderStyle-BackColor="LightBlue" HeaderStyle-ForeColor="#990000" HeaderText="Employer Contribution" />
                    <asp:TemplateField ItemStyle-Width="40" HeaderStyle-BackColor="White" HeaderStyle-ForeColor="White" HeaderText="" />
                    <asp:HyperlinkField Text="PlanProfile" DataNavigateUrlFields="plandetails.htm?plan={1}"  HeaderStyle-BackColor="LightBlue" HeaderText="Quoted Plan<br />(Click plan to view details)" />

            </Columns>
       
        </asp:GridView>

And here's the code-behind method being called:

    public void getData()
    {
        SqlConnection conn = new SqlConnection(_dbConnection);
        conn.Open();
        try
        {
                    SqlCommand command = new SqlCommand("ITDB.dbo.spSOMCAgentWebQuote_sel", conn);
                    command.CommandType = CommandType.StoredProcedure;
                    command.Parameters.Add(new SqlParameter("@ProposalID", SqlDbType.Int));
                    command.Parameters.Add(new SqlParameter("@RatepageCategoryID", SqlDbType.Int));
                    command.Parameters.Add(new SqlParameter("@EECount", SqlDbType.Int));
                    command.Parameters.Add(new SqlParameter("@ESCount", SqlDbType.Int));
                    command.Parameters.Add(new SqlParameter("@EFCount", SqlDbType.Int));
                    command.Parameters.Add(new SqlParameter("@ECCount", SqlDbType.Int));
                    command.Parameters.Add(new SqlParameter("@EmployerContributionID", SqlDbType.Int));
                    command.Parameters[0].Value = _proposalID;
                    command.Parameters[1].Value = _ratepageCategoryID;
                    command.Parameters[2].Value = _eeCount;
                    command.Parameters[3].Value = _esCount;
                    command.Parameters[4].Value = _efCount;
                    command.Parameters[5].Value = _ecCount;
                    command.Parameters[6].Value = _employerContributionID;

                    SqlDataReader dataReader = command.ExecuteReader();

                    dataReader.Read();

                    this.gvPlanList.DataSource = dataReader;
                    this.gvPlanList.DataBind();

        }
        catch {
        }
        finally
        {
            conn.Close();
        }
    }