Private Membership Levels

I spent most of the day installing and configuring the Membership plugin on my site. For the most part, it worked great, but I'm still encountering one small issue.

I would like to have three membership levels that get populated manually. I created both Subscription Plans and Access Levels for these three groups. I then activated the Subscription Plans and switched them to private. When I attempted to create a new user, the private levels were still showing up and I was able to register for them (which I do not want).

My guess is that I just misunderstood the language in the plugin. Is there a way to achieve this setting? If so, could somebody please offer me some direction?

Thanks in advance!
David