If I have this figured out correctly, you could delete your FPs for your last day onsite right now and look for (and book) new FPs for your first day in the parks on the 27th (HS). Then the next day (morning of the 28th), you could try and book FPs for your last day onsite. Not sure how hard to get the FPs you had booked for your last day, but I can't think of another way to have FPs booked in advance for all of your days (other than cancelling FPs for a different day during your week instead of the last day in the above scenario). Good luck!