Question! how i can add a sidebar on the register page

Is your registration area already setup and using an Itemid, or are you asking how to add a module to the registration page?

Honestly, the best option would likely be to create a template override of the standard Joomla registration page and add your text in manually.. instead of doing it in a module. That will prevent any extension (not just SCLogin) that may be linking to the 'default' registration page, and not your specialized one using a menu item.

To create a template override, simply copy /components/com_users/views/registration/tmpl/default.php to /templates/<YOUR_TEMPLATE>/html/com_users/registration/default.php
You may have to create some of those directories (html, com_users, registration). Once that file has been copied, edit it directly in the /templates folder and Joomla will use it instead. All your changes will be saved when you update Joomla as well.

I hope that helps, but if not, let us know!

Thanks,
Alex