Can't seem to upload file using multipart/form-data in C#

I'm trying to upload an image to Imgur's api https://api.imgur.com/3/upload but return status: 400, Bad request BadReqImg.

I'm convinced the issue is coming from file uploading part, as below, but couldn't find any problem with it.

if (files != null)
            {
                foreach (string key in files.Keys)
                {
                    string filePath = @"C:\Image\" + files[key];
                    if (File.Exists(filePath))
                    {
                        int bytesRead = 0;
                        byte[] buffer = new byte[2048];
                        byte[] formItemBytes = System.Text.Encoding.UTF8.GetBytes(string.Format("Content-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"\r\n", key, files[key]));
                        memStream.Write(boundarybytes, 0, boundarybytes.Length);
                        memStream.Write(formItemBytes, 0, formItemBytes.Length);

                        using (FileStream fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read))
                        {
                            while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
                            {
                                // Write file content to stream, byte by byte
                                memStream.Write(buffer, 0, bytesRead);
                            }

                            fileStream.Close();
                        }
                    }
                }
            }

Here's the entire code

string Url = "https://api.imgur.com/3/upload";
        string retString = string.Empty;
        NameValueCollection values = new NameValueCollection();
        NameValueCollection files = new NameValueCollection();

        values.Add("name", "testpic");
        files.Add("image", file);

        try
        {
            string boundary = "-------------------------" + DateTime.Now.Ticks.ToString("x");
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url);
            request.ContentType = "multipart/form-data; boundary=" +
                                    boundary;
            request.Method = "POST";

            Stream memStream = new System.IO.MemoryStream();
            var boundarybytes = System.Text.Encoding.ASCII.GetBytes("\r\n--" + boundary + "\r\n");
            var endBoundaryBytes = System.Text.Encoding.ASCII.GetBytes("\r\n--" + boundary + "--");

            #region 2
            foreach (string key in values.Keys)
            {
                // Write item to stream
                byte[] formItemBytes = System.Text.Encoding.UTF8.GetBytes(string.Format("Content-Disposition: form-data; name=\"{0}\"\r\n\r\n{1}", key, values[key]));
                memStream.Write(boundarybytes, 0, boundarybytes.Length);
                memStream.Write(formItemBytes, 0, formItemBytes.Length);
            }

            if (files != null)
            {
                foreach (string key in files.Keys)
                {
                    string filePath = @"C:\Image\" + files[key];
                    if (File.Exists(filePath))
                    {
                        int bytesRead = 0;
                        byte[] buffer = new byte[2048];
                        byte[] formItemBytes = System.Text.Encoding.UTF8.GetBytes(string.Format("Content-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"\r\n", key, files[key]));
                        memStream.Write(boundarybytes, 0, boundarybytes.Length);
                        memStream.Write(formItemBytes, 0, formItemBytes.Length);

                        using (FileStream fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read))
                        {
                            while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
                            {
                                // Write file content to stream, byte by byte
                                memStream.Write(buffer, 0, bytesRead);
                            }

                            fileStream.Close();
                        }
                    }
                }
            }
            #endregion

            memStream.Write(endBoundaryBytes, 0, endBoundaryBytes.Length);
            request.ContentLength = memStream.Length;

            using (Stream requestStream = request.GetRequestStream())
            {
                memStream.Position = 0;
                byte[] tempBuffer = new byte[memStream.Length];
                memStream.Read(tempBuffer, 0, tempBuffer.Length);
                memStream.Close();
                requestStream.Write(tempBuffer, 0, tempBuffer.Length);
            }

            using (var response = request.GetResponse())
            {
                Stream stream2 = response.GetResponseStream();
                StreamReader reader2 = new StreamReader(stream2);
                retString = reader2.ReadToEnd();
            }
        }
        catch (Exception ex)
        {

        }

        return retString;