domain.com loads fine but adding 'www' takes me to nginx startup page

I can't figure it out for the life of me.

mydomain.com loads the website perfectly fine but if i do www.mydomain.com it loads the "Welcome to Nginx" page. I either deleted a line I shouldn't have by accident or I'm missing something incredibly simple. If anyone has any idea what I missed, I would love you forever.

Any help is greatly appreciated.