I thought Fajr was called at 4:00 so at 3:59 I ran and srank water and woke up my family to drink before we supposedly were to hear it, and then I looked up prayer times after minutes passed with no azan heard, and it turns out Fajr was at 3:48, what do I do now?
You do not have to make up that day. Indeed, Al-Bukhari narrates a similar incident at the time of the Prophet ﷺ
حَدَّثَنِي عَبْدُ اللَّهِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ فَاطِمَةَ، عَنْ أَسْمَاءَ بِنْتِ أَبِي بَكْرٍ ـ رضى الله عنهما ـ قَالَتْ أَفْطَرْنَا عَلَى عَهْدِ النَّبِيِّ صلى الله عليه وسلم يَوْمَ غَيْمٍ، ثُمَّ طَلَعَتِ الشَّمْسُ. قِيلَ لِهِشَامٍ فَأُمِرُوا بِالْقَضَاءِ قَالَ بُدٌّ مِنْ قَضَاءٍ. وَقَالَ مَعْمَرٌ سَمِعْتُ هِشَامًا لاَ أَدْرِي أَقْضَوْا أَمْ لاَ.
Narrated Abu Usama from Hisham bin Urwa from Fatima: Asma bint Abi Bakr said, "We broke our fast during the lifetime of the Prophet (ﷺ) on a cloudy day and then the sun appeared." Hisham was asked, "Were they ordered to fast in lieu of that day?" He replied, "It had to be made up for." Ma`mar said, "I heard Hisham saying, "I don't know whether they fasted in lieu of that day or not." (Sahih al-Bukhari, 1959)
Scholars have explained this hadeeth saying that "It had to be made up for" was the opinion of Hisham bin Urwa who was narrating the hadeeth from Fatima who was narrating from Asmaa bint Abu Bakr. Scholars add that if they had to make up for the that day, they would have made it up, and we would have heard about it.
When Muslims do their best to follow the orders of Allah, but they in the process make a mistake, Allah subhanahu wa ta’alla overlooks their mistakes.
إن اللهَ تجاوز عن أمتي : الخطأُ، والنِّسْيانُ، وما استُكْرِهوا عليه > الراوي : عبدالله بن عباس | المحدث : الألباني | المصدر : تخريج مشكاة المصابيح الصفحة أو الرقم: 6248 | خلاصة حكم المحدث : صحيح بمجموع طرقه
On the authority of Ibn Abbas (may Allah be pleased with him), that the Messenger of Allah (peace and blessings of Allah be upon him) said: Verily Allah has pardoned for [or been lenient with] my ummah: their mistakes, their forgetfulness, and that which they have been forced to do under duress. (Deemed Saheeh by the Al-Albani, 6248)
Please see this link for more information https://islamqa.info/en/27227