Hold my beer

We signed up for the 10:30-11:00 staggered boarding time on the Dream a couple months ago and it showed we were confirmed on the boarding passes. (Wish I had printed them). http://www.healthyfoodplans.net/2016/01/press-these-4-points-on-your-body-to-accelerate-your-metabolism-and-lose-weight-fast.html we got a call from carnival today telling us we need to sign up for a check in time. Well the only time available is 2:30-3:00. We are planning to park at the Erato terminal. I have heard that it could be full for late boarding people. Does anyone know anything about this situation. I'm wondering if we need to look at other options.

We are leaving this Sunday. Any help would be appreciated