Need opinions

So, for this fall semester, Last tuesday I accepted my AID, it was about 3.6k and 3.6k for my spring semester. Which ended up for this semester around 999 hundred for books ect. So I bought 3 books that I needed with the AID. Which ended up leaving me with around 800 hundred or less since the books were 193 in total. And now I see that They added more funds to my AID. About 1.6 more. Which now I have left 1.9k left for this semester. How does that happen? My theory is that because the books left me with low left over to cover other expenses but what might be the reason?

Pd: I am very grateful for the AID because I know many ppl don’t receive anything. Seriously 🥲