GoLang with GoDaddy certificate not configured correctly

in general I got 3 files from GoDaddy:

1. main Certificate file
2. Server Private Key
3. Bundle file

in configured all these files in my Go server in the following way:

    pem, err := ioutil.ReadFile("cert/sf_bundle-g2-g1.crt")
    if err != nil {
        log.Fatalf("Failed to read client certificate authority: %v", err)
    }
    if !certpool.AppendCertsFromPEM(pem) {
        log.Fatalf("Can't parse client certificate authority")
    }
    tlsConfig := &tls.Config{
        ClientCAs:    certpool,
    }

    srv := &http.Server{
    Addr: "myalcoholist.com:443",
    Handler: n,
    ReadTimeout: time.Duration(5) * time.Second,
    WriteTimeout: time.Duration(5) * time.Second,
    TLSConfig: tlsConfig,
}
err := srv.ListenAndServeTLS(config.CfgIni.CertificateFile,config.CfgIni.PrivateKeyFile)

The web server runs properly, it's currently published at https://myalcoholist.com:443.

I validated my SSL using https://www.ssllabs.com/ssltest/analyze.html?d=myalcoholist.com and it's response is This server's certificate chain is incomplete. Grade capped to B.

you can go to this link to see the all detailed result.

what am I missing ?