draw chart in excel

hi

I have two columns of numbers (x , y)

this numbers exporting to excel and after drawn chart by this numbers.

but i have 2 series in chart 

when i right click on chart in excel and click on change chart type exists 2 series

but i wanna just one series

my cod:

Microsoft.Office.Interop.Excel.Range chartRange;

                Microsoft.Office.Interop.Excel.ChartObjects xlCharts = (Microsoft.Office.Interop.Excel.ChartObjects)worksheet.ChartObjects(Type.Missing);
                Microsoft.Office.Interop.Excel.ChartObject myChart = (Microsoft.Office.Interop.Excel.ChartObject)xlCharts.Add(100, 80, 400, 400);
                Microsoft.Office.Interop.Excel.Chart chartPage = myChart.Chart;

                chartRange = worksheet.get_Range("A1", "B100");
                chartPage.SetSourceData(chartRange, System.Reflection.Missing.Value);
                chartPage.ChartType = Microsoft.Office.Interop.Excel.XlChartType.xlXYScatterSmoothNoMarkers;

thanks