Existing site added to multi-site not working properly

I have added my existing site to Multisite. It shows the new site i-cancorp.com in the roster but I have to login separately. When I do, it does not show the other sites listed in the roster. It still seems to be functioning as its own site. A few things that are different for this site is, it is already on my A2 server account and has its own cpanel. I have already transferred the files to another domain, so I am not opposed to starting fresh. Do I need to remove it from the server or could I just map it to a sub-domain?