Why a new blank line is inserted when i select Save option from the context menu on Treeview

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C#2.0

C#

WinForms

I write the code to save the data from datagrid to the text file as follows

private void Save_Click(object sender, EventArgs e)
{
    string filedata = string.Empty;
    string strcontent = string.Empty;
    string srEnd = string.Empty;
    if (dataGridView1.Rows.Count > 0)
    {
        m_flag = true;
        if (m_flag)
        {
            StreamReader sr = new StreamReader(Append.FileName);
            while (sr.Peek() >= 0)
            {
                srEnd = sr.ReadLine();
                if (srEnd.StartsWith("9"))
                {
                    strcontent = srEnd;
                }
            }
            sr.Close();
            StreamReader srNew = new StreamReader(Append.FileName);
            while (srNew.Peek() >= 0)
            {
                filedata = srNew.ReadToEnd();
                if (strcontent != string.Empty)
                    filedata = filedata.Replace(strcontent, "");
            }
            srNew.Close();
            StreamWriter swwrite = new StreamWriter(Append.FileName);
            swwrite.Write(filedata);
            swwrite.Close();
            m_flag = false;
            sr.Close();
        }

        if (m_flag == false)
        {
            List<string> lstContent = new List<string>();
            foreach (DataGridViewRow row in dataGridView1.Rows)
            {

                if ((string)row.Cells[0].Value == "FileControl")
                {

                    lstContent.Add((string)row.Cells[1].Value);

                    string mydata = string.Join(",", lstContent.ToArray());

                    using (StreamWriter sw = new StreamWriter(Append.FileName, true))
                    {
                        sw.WriteLine();
                        sw.Write(mydata);
                    }
                }
            }

        }
    }
}

My actual process is i will have a text file attached to a tree node. If the user fill the form and click on save i will save the text file as well as i will show the data in the datagrid. While writing to datagrid i will add a new line which was changed according to the entries by user.

Each and every length should be 94.

I am having 2 issues here

1) When i click save for multiple times a new line is created in my text file that i am writing my data.

2) If my data in the datagrid is as follows

101 111111111 1111111111010210452A094101
9000001000001000000010011111111000000000001000000000000
It works fine if i have some more data

101 111111111 1111111111010210452A094101
52001 1 1 CCD1 101021101021 1111111110000001 6201111111181 00000000011 1 1 0111111110000001 820000000100111111110000000000000000000000011 111111110000001 9000001000001000000010011111111000000000001000000000000
It is breaking some of the characters from the first line.

can any one help me please.