When registering on a subdomain site, user is taken to main site registration

I have my main site set up to accept new site owners. However on the site of a new site owner it seems that for a user to register, they are taken to the registration page for the main site.

I would like users who visit one of my subdomain sites to register for that site only. The concept is I am providing a website solution for professionals to create a website. On their site, they should be able to have users sign up. The main site is the site where the professional comes to sign up for their own site. Make sense?