If your pet had a first rabies vaccination at the six-week mark, the 21-day waiting period clears around now, which is worth double-checking against the actual vaccination date rather than assuming it's exactly 21 days from when you booked the appointment.
This is also the point to lock in transport if you haven't already — book a Renfe pet seat if you're training in, confirm a ferry operator's pet accommodation option if you're island-bound, or check an airline's cabin pet allocation, all of which can fill up closer to travel. If you're flying, confirm your specific airline accepts pets in the hold if that's what your trip needs — not every carrier does.
Confirm pet-friendly accommodation is actually booked and the pet policy is in writing, not just assumed from a listing's general description — under Spain's animal welfare law a property should have this in writing already, but message a casa rural, Airbnb host, or hotel directly if the listing itself doesn't spell out fees and restrictions clearly.