BCG Alternate?

Hi all, I go to a top target and found out yesterday I made the alternate list for BCG's first round interviews. They don't give us an option to sign up ourselves if there are spots open, the recruiting team will contact us if anyone cancels. I guess I am wondering more about this because I hadn't heard of it. Do they put a lot of people on the alternate list? Is it more likely I won't make it off the list, and would it be worth it to reach out to the recruiter? Thanks