OP didn't say specifically, but I surmise they are in the St. Mary campground. We stayed in the Rising Sun campground a couple years ago. No reservations accepted there, so you had to be there by 9 a.m. if you wanted a site that day. MAYBE, the OP was there, and wanted a different campground. Don't know.
But, don't knock him for reserving 3 days out. Maybe they are on a flexible schedule, and didn't know when they would be there. Not everyone has each stop planned to the hour (okay, I do, but I have a DW that is not quite as understanding about changed plans). Some folks are fortunate enough to have flexibility.