how do I make friends

Hi guys, this September I moved to a new school (I’m going into grade 11). I’ve found a group of girls to eat lunch/hang out with during school but were nothing more than school “friends”. I recently found out that they have a whole groupchat where they schedule days to hangout on weekends/after school. I’m not upset that I’m not in the group chat because I am new after all and I don’t know any of these girls well enough to be even considered friends. With that being said, there is this one girl in the group that is also new to the school so me and her got along really well naturally. Things were going good until I saw on Sunday the whole group (except me) posting cute pictures togethor in fancy dresses for one the girls birthday. I’m not even that hurt that I wasn’t invited because it makes sense, what I am hurt about is that the other new girl was there and I wasn’t. I seriously don’t know what I’m doing wrong. Why are they accepting her and not me? She’s probobky also in the group chat. And this is no shade to the new girl because I really like her but what am I doing wrong 🙁. Before you say “you should just ask to be invited next time”. I really hate it when people self invite themselves to events so I don’t want to be that guy. And my feelings would honestly be hurt more if they said no so I’d rather not ask. How do I get these girls to like me and become friends with me?