C# MemoryStream to text file not Completing

I'm having an issue with using a memory stream on a large text file function in C#. The output text file doesn't contain all the information, it's missing the last few lines of text that I wrote to it in streamwriter.

Many of the posts say to use stream.flush() and reset the stream to the beginning of the stream using stream.seek(0, seekOrigin.End), but neither seem to make a difference.

Here is the code:

using (var stream = new MemoryStream())
        {
            using (var sb = new StreamWriter(stream))
            {
                Decimal[,] oparray = new decimal[477, 521];

                List<Rech_RCH_Result> result1;

                //RCH File Header
                sb.WriteLine("#MODFLOW2000 Recharge Package");
                sb.WriteLine("PARAMETER 0");
                sb.WriteLine("         1        50");

                for (int sp = 1; sp < 3; sp++)  //should be 209
                {
                    ObjectResult<Rech_RCH_Result> qryRCH = db.Rech_RCH(NRD, sp);

                    result1 = qryRCH.Select(p => new Rech_RCH_Result { M_Col = p.M_Col, M_row = p.M_row, Recharge = p.Recharge, StressPeriod = p.StressPeriod }).ToList();

                    //Stress Period Header for SP
                    sb.WriteLine("         1         1");
                    sb.WriteLine("        18     1.000(10e15.6)                   -1     RECHARGE");

                    //model row = 1 to 476, col = 1 to 520
                    foreach (Rech_RCH_Result s in result1)
                    {
                        oparray[s.M_row.Value, s.M_Col.Value] = s.Recharge;
                    }

                    for (int x = 1; x < 477; x++)
                    {
                        for (int y = 1; y <= 520; y += 10)
                        {
                            //write out values in chunks of 10
                            sb.WriteLine(string.Format("   {0:0.000000E+00}   {1:0.000000E+00}   {2:0.000000E+00}   {3:0.000000E+00}   {4:0.000000E+00}   {5:0.000000E+00}   {6:0.000000E+00}   {7:0.000000E+00}   {8:0.000000E+00}   {9:0.000000E+00}", oparray[x, y], oparray[x, y + 1], oparray[x, y + 2], oparray[x, y + 3], oparray[x, y + 4], oparray[x, y + 5], oparray[x, y + 6], oparray[x, y + 7], oparray[x, y + 8], oparray[x, y + 9]));
                        }
                    }

                    Array.Clear(oparray, 0, oparray.Length);
                }

                stream.Flush();
                //Looks like the stream is not completing and missing a few lines.
                //stream.Seek(0, SeekOrigin.Begin);
                stream.Seek(0, SeekOrigin.End);


                using (FileStream file = System.IO.File.Create(Server.MapPath(string.Format("~/RCHFiles/{0}.txt", filename))))
                {
                    stream.WriteTo(file);
                }

                //using (ZipFile zip = new ZipFile())
                //{
                //    zip.AddEntry(filename + ".RCH", stream);
                //    zip.Save(Server.MapPath(string.Format("~/RCHFiles/{0}.zip", filename)));
                //}
            }
        }