You can try to go earlier; they may or may not be able to accommodate you. I once went an hour before our reservation time and asked if they could push back my meal by 30 minutes (it conflicted with the parade time); they just offered to make it immediately instead... so it's possible. If they're busy, though, I imagine they'll ask you to come back at your allotted time.
I don't recall what time they start serving F! meals, but it may not even have started yet at 3, though...