First, do not make revisions in bp-default theme. Revisions will be overwritten when BP is upgraded.
Instead,
- create a child theme of bp-default theme, e.g. mybpproject,
http://codex.buddypress.org/theme-development/building-a-buddypress-child-theme/
- create a functions.php file and put it in your child theme folder. Define new widget/s here (name, ID, etc)
- copy over the template file from bp-default theme to your child theme folder (following directory structure) then add the call to dynamic_sidebar in that template.