domain mapping showing www. not without

So I turned maindomain.com into a WordPress MultiSite installation using subdomains. It works peachy, the problem…

Let’s say I created remotecontrol.maindomain.com so I can domain map remotecontrol.com into it.

https://www.remotecontrol.com is working, however when I type remotecontrol.com (without the www.)….
https://maindomain.com/wp-signup.php?new=remotecontrol.com shows up (maindomain.com and remotecontrol.com are just example domains for this post).

How do I fix this?