how do i join my friend's friend group?

so im a junior in college and i literally only have 1 close friend (i'll call her A) that i talk/text regularly and we've been friends since freshman year, but she's close with other people (more?) and she knows that i only have her. i've asked A to hang out multiple times this semester, but we never went through with them, and she hangs out with her other friends a lot. i wish i could join her group and befriend her friends as well. i've only seen/hung out with some of them 2-3 times and i never see them around campus. i see photo dumps she posts on her finsta and i feel really lonely...

would that be a wise choice? how should i ask her? and how can i imply that it's not just once, but i want to be a part of their friend group? i'm scared A doesn't want me to join her group and will feel uncomfortable with me asking her. sometimes i feel like she doesn't want to hang out with me at all... while having lunch today, A's friend casually asked her if she's having her b-day party on a certain date and discussed some of the plans for that day right in front of me. and i realized i wasn't invited. she also never asks me to hang out. it's always me who initiates and it makes this relationship seem very one-sided, but not at the same time because we still do have a good relationship for the most part.

*just to note: while A was abroad, i tried getting closer to one of her friends i met through A and hung out a couple times with, asking if she wanted to join this club with me again, but she declined and i realized she was only in there because of A and didn't want to join just with me... (it was a social club, nothing serious or mandatory)

im really introverted and i feel like others view me as unsociable.. i just don't know what to say in a conversation and what to talk about regularly. any tips on getting closer to people on more than the surface level? especially if we don't exactly share any hobbies