My gf (18F) always spoils my mood (18M) whenever we go for hangout

Since last two hangouts we are always going home with spoiled mood even tho however our day was gone. During the 1st hangout I was solving a math quiz and it was urgent so in between our hangout I have to do it and after it was done she was not replying me with excitement. I asked her whats wrong so many times I explained her that I had to do it or my marks will get deducted said sorry so many times tried to pamper her but she was not ready to understand me idk why and today we were watching a movie and since the start of the movie my gf was saying she has to reach hostel early by 8:30 pm I told her reassured her that I’ll drop you by the hostel on time. In between the movie I told her again and again that i’ll drop you on time i’ll drop you on time enjoy the movie dont think too much (not once i scolded her) I said everything in loving way.Then we went to a cafe for dinner and still she was thinking about reaching hostel early. And its not today every hangout its the same thing.I was yapping to her and she was giving so dry replies to me i asked her whats wrong she said she’s thinking about same thing again. I was so sad than I dropped her home on time but Im kinda sad thats its always the same thing

tl;dr : Lately, every hangout with my girlfriend ends with a bad mood. Once, I had to quickly finish an urgent math quiz, but she stayed upset even after I apologized. Today, she kept worrying about getting back to her hostel on time, which happens almost every time we go out, and she gave me dry replies the whole evening. I’m feeling sad because no matter how good the day starts, it always ends the same way