Wa Alaykum Assalam Brother.
Prophet Mohammad Said that:
Whoever does not have the intention of fasting from the night before, then there is no fast for him. 22:245
However, the scholars differed in this case as follows:
It says in al-Mawsoo‘ah al-Fiqhiyyah (40/275):
The Hanafis, Shaafa‘is and Hanbalis are of the view that forgetting to form the intention on some nights of a fast that must be observed on consecutive days interrupts the sequence, as does omitting it deliberately, and forgetting is not regarded as a valid excuse for failing to do what is obligatory.
The Maalikis are of the view that a single intention is acceptable for every fast that must be observed on consecutive days, such as Ramadan.
In al-Khulaasah al-Fiqhiyyah ‘ala Madhhab as-Saadah al-Maalikiyyah, it says:
A single intention is sufficient for every fast which must be observed on consecutive days, such as Ramadan.
So as you can see, the majority agreed that you should intend to fast every night. Imam Malik however agreed that one intent before Ramadan to fast the whole month is sufficient.
So Unless you intended to fast the whole month before Ramadan, you should make up for this day.
Allah knows best.