SSL ignored on subdomains

I have an SSL certificate only for the top level domain (e.g. https://mycompany.com) and have a subdomain (http://blog.mycompany.com) that points via DNS to a blog on Tumblr.

My nginx server config looks like this:

server {
        listen 80;

    server_name mycompany.com;

    return 301 https://mycompany.com$request_uri;
}


server {
    listen 443 ssl;
    listen [::]:443 ipv6only=on;

    ssl on;
    ssl_certificate  /etc/nginx/ssl/ssl.cer;
    ssl_certificate_key /etc/nginx/ssl/ssl.key;

    # Add perfect forward secrecy
    ssl_prefer_server_ciphers on;

    # Add HSTS
    add_header Strict-Transport-Security "max-age=31536000; includeSubdomains";

    ssl_protocols TLSv1 TLSv1.1 TLSv1.2;

    ssl_ciphers 'ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:AES:CAMELLIA:DES-CBC3-SHA:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!aECDH:!EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA';

    server_name mycompany.com;

    location / {
        proxy_pass http://localhost:3001;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;
    }
}

My DNS record looks like this:

CNAME blog domains.tumblr.com.

If I try accessing http://blog.mycompany.com then it gets redirected to the https version and there’s a Server Not Found error in my browser. Do I need to make changes to the DNS records or in Nginx?