Must I make up the fast after having eaten, thinking that the Maghrib call to prayer had been given, only for it to become clear that the matter was uncertain?

Scholars differ regarding one who ate or drank, thinking that the sun had set, and then it became clear that it had not yet set. The majority of scholars hold that making up the fast is obligatory. This is based on the apparent statements of An-Nawawi, Al-Izz ibn Abdus-Salam, Az-Zarkashi, As-Suyuti, Ibn Qudamah, and many verified opinions from the Hanafis and Malikis. This is also because the default rule is to remain in the previous state, and according to the jurisprudential maxim: "No consideration is given to a conjecture whose error has become manifest."

However, Shaykh al-Islam Ibn Taymiyyah and some verified scholars chose the view that making up the fast is not obligatory, based on the Almighty's saying: "And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended. And ever is Allah Forgiving and Merciful." (Al-Ahzab 5).

As for one who did not become aware of anything (i.e., did not realize the error), there is no making up of the fast required of them, as stated by many scholars. Therefore, you are not obligated to make up that day.