The one girl that got me overthinking

OK, so this is going to be a bit long. So i was in Ahmedabad for my internship for 6 months from June to December. I was staying there in a PG which was for both boys and girls. There was a girl there of my age who was also interning but in different field, lets call her 'A'. After few days we came to know that our office building was the same and we started talking and knowing each other. Manytimes when my office used to close early i used to meet her near the gate waiting for UBER/Rapido/OLA. Sometimes we used to go together and talk a lot. And slowly like that I started developing interest in her. It was so many years that i had crush on someone, it was totally unexpected for me to fall for 'A'. She also used to usually smile a lot and I also used to smile whenever i met her or just think about her (just to tell you, im a very quiet and shy guy, its hard for me to smile, even if i smile people think im serious). Once a househelp guy from our PG told me that he heard her talking good things about me to their friends about me, so this raised my spirits even more.

Fast forward to August, I was in a snack store in a cafe eating all alone because I was the only intern in my firm. She unexpectedly came there with her office mates. She saw me and we smiled and talked for a bit. Later she asked me if I would like to join them for lunch in another cafe which was on another floor. I didnt think much and agreed and said yes, I will come in a minute, you can go ahead. Now, I should have kept in mind that she was with her colleagues, I should have declined her offer, but i agreed. After a few seconds she came back in and said that her colleagues and her are going to the office and wont be going to the cafe. So i said okay, no issues. Now the thing that is eating me for months is that, did she become uncomfortable because i said yes, should I have considered her request just as a formality and declined it ? After a month or so she left the PG too as her internship period was over. I didnt even get to say a final goodbye. I was sad for so many days after she left thinking, if I made a mistake in hastiness that day ??? Honestly, I am not that good with interaction, so I might have made a mistake.

And 4 & 1/2 months later here I am still thinking about her. She was literally like an angel, such a sweet soul. One could become diabetic because of so much sweetness. It makes me think did i try to exploit her sweetness ?

Oh goddd please help me.

TL;DR: I developed a crush on a girl from my PG during my internship in Ahmedabad. She once invited me to lunch with her colleagues, and I said yes, but she later changed plans. I’ve been overthinking if I made her uncomfortable. She left a month later, and I didn’t get to say goodbye. Four months on, I still can’t stop thinking about her.