Not sure what you mean by “confirmation link” after they sign up. Do you just mean the confirmation message that says they have been signed up?
There are also a couple of other alternatives:
4) Put your long description into the sheet description itself instead of above the shortcode on the page. Then, when you click on sign-up, that description won’t show. After signing up, the confirmation message will then be on top of the long description.
5) Check the setting for “Redirect Sign Ups to Main Page?” and set up a main volunteer page with the basic shortcode (no arguments), and no other page content, and set that page in the drop down list above that check box option. Now, when somebody clicks on a sign-up link, they will be redirected to that page for the sign-up form.