question re block element right sidebar

Hi
I am trying to create a block element right sidebar to be displayed on 1 page only. I want it to be a custom sidebar displaying content different to the right sidebar on the other pages.

I have set the location to Page and the title of the page I want which is Youtube
I have set the element type as right sidebar

On the Youtube page I am creating I am using both sidebars to the left of the page. However all other pages have the right sidebar on the right of page and I want to keep all that sidebar content.

My worry is that I have this message:

This will remove the current sidebar widgets for the selected sidebar. Your layout must have a sidebar set for this Element to show.

Does the fact that I have specified the location as 1 page only mean that the changes will only be applied to the right sidebar on that single page?
I do not want to lose all the content on my default sidebar.
Thanks