.htaccess concatenating www + subdomain
If I understand you correctly, you want to redirect everyone to the www version of the site.
How about this.

RewriteCond %{HTTP_HOST} !^www.example.com$ [NC]
RewriteRule ^(.*)$ http://www.example.com/$1 [R=301,L]


It will redirect anything that isn't www.example.com to www.example.com and pass along the url.

http://httpd.apache.org/docs/2.4/rewrite/intro.html has more options you can use.