It turned out I was looking at the wrong default file, it's supposed to be in sites-enabled.
I filled in the missing s, and ran sudo nginx -t and got the following message
nginx: [warn] conflicting server name "domainname.com" on 0.0.0.0:80, ignored
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful
my site is still not up on the domain
what is this conflict it's telling me?
Edit: Ok, so I've removed all files in sites-enabled and sites-available. Started over. Created a file in sites-available again. Then ln -s it to sites-enabled.
All [warn] lines disappeared. Configuration of nginx.conf was successful.
Then I tried sudo service nginx reload. Got the same message: reload: Unknown instance: 😞
Edit: I've rebooted my droplet. Reloading nginx was successful. My site is now up on the domain.