How to automatically associate registered users to a specific membership level?

Hello Guys!

I'm running a BP+WPMU Project with Membership enabled.

I've created 3 member levels:
Visitor: Working exactly as I need
User: Can do some things but do not create blog.
Blogger: Can do everything.

The problem is that when the user register to my site through buddypress registration form, if user do not click on "Yes I want to create a site" this user is associated to User membership level, and if the user clicks on the message the user is associated to Blogger membership level.

What I have now does not associate user who creates an account at my site to any level... So, how can I associate the user?