Setting up an SSL on Multisite

I have bought an SSL certificate for my site so people can order sites from me, however the SSL is not showing as active on the site. Sites are generated as follows:

My main site where users can sign up etc - http://www.mydomain.com

Users sites go to - user1.mydomain.com etc

How do I get the SSL to feature on the main domain name? Have a bit of bother trying to set this up, whenever I go to domain mapping plugin and click on force SSL it breaks the site.

Any advice would be great!

Thanks