@Ingeborg *******
Visit Immigration and apply for the 30-days extension. . . . . . . I would add: It is highly possible that the Immigration officer wants to see a TM30.
The TM30 is the registration of your accommodation provider/hotel/guesthouse/resort, which must be done within 24 hours of your arrival at the place where you will be staying
In case you stay privately at a friend’s house, or use an AirBnB, the friend or the landlord needs to register you in the TM30 system and you will need a printout or screenshot of the receipt
Usually the officer, when he is entering your personal data in his computer, he will see that you were registered by the hotel. It would be advisable to carry a business card of your hotel