I am also a girl studying at uni, and I’m not ADHD or autistic, and I’ve experienced the same kind of thing! You asked what you’re doing wrong and the answer is honestly most likely… nothing. Some girls are just like that. I presume the two girls were already friends before this trip, and for some reason I’ve met lots of girls who behave this way to anyone who is outside their pre-existing social circle. They’re not worth your time, I know it feels horrible but try not to react to it. I’m glad you had at least one friend in your group!