try to ask that girl you know outside of your lunch table. if she says no, then are you able to talk to some people during class and ask them if u can sit with them today. then if it goes well, u can start sitting with them. Or can u sit in another part of the school, like outside for lunch?
also u said the 2 girls went away today. so maybe tomorrow theyll sit with you and the other girl again?
good luck i know what it feels like to have little friends in school, and it sucks.
"Don't ever, for any reason, do anything, to anyone, for any reason, ever, no matter what, no matter where, or who, or who you are with, or where you are going, or where you've been, ever, for any reason whatsoever." -Michael Scott