Ok, so after looking at this picture
(credits to @Hafo)
If I'm not mistaken, the 3 friends Bocchi has left are 12, 17 and 29.
12 is Yamada Hanako, Aru's friend from the tennis club.
17 is the gyaru looking girl and 29 is the short hair girl who sits in front of Minagawa Rau, you can see...