Have you changed the nameserver settings on your domain name? That's normally the cause of this sort of thing.
What you are seeing is a kind of "default" holding page that gets put up by your domain registrar that covers any new domains until they are pointed to a different hosting server. That site will continue ot be shown until you point your domain name to your own hosting account.
You will have received the nameserver details from Hostgator in your normal welcome email. You'll find details for Nameserver 1, Namesever 2, and possibly Nameserver 3. You need to set these values for your domain name. Your domain registrar can help with that. When that's done, it's normalyl between 2 and 48 hours for the settings to propegate around the world and you'll be able to see your site.