Webclient equivalent of CURL command

I am trying to upload a file via a POST to a REST API in a c# winform.

If I run the following command with curl the file is uploaded successfully:

curl.exe -H "Content-type: application/octet-stream" -X POST http://myapiurl --data-binary @C:\test.docx

I have tried using WebClient in my WinForm:

using (var client = new WebClient())
            {
                client.Headers.Add("Content-Type", "application/octet-stream");

                byte[] result = client.UploadFile(url, file);
                string responseAsString = Encoding.Default.GetString(result);
                tb_result.Text += responseAsString;
            } 

But I just get a (500) Internal Server.

Checking this with fiddler the following headers are added with CURL:

POST http://myapiurl HTTP/1.1
User-Agent: curl/7.33.0
Host: 10.52.130.121:90
Accept: */*
Connection: Keep-Alive
Content-type: application/octet-stream
Content-Length: 13343
Expect: 100-continue

But checking my WebClient method shows the following:

POST http://myapiurl HTTP/1.1
Accept: */*
Content-Type: multipart/form-data; boundary=---------------------8d220bbd95f8b18
Host: 10.52.130.121:90
Content-Length: 13536
Expect: 100-continue
Connection: Keep-Alive

How can I simulate the CURL command above from my app?