For what it’s worth, I think resting bitch face is a myth. But if you have it… who cares!
You shouldn’t be required to keep a fake, pleasant expression for other people’s benefit. Women are always encouraged to be friendly and conciliatory. Telling someone that there is something wrong with their face is so damaging. Especially when multiple people are in on it.
You could just have trouble getting to know people because you’re shy. Maybe being told again and again that you look “mean” and off-putting has made it worse. That kind of thing would make anyone doubt themselves, especially if you hear it from a number of people. I think it’s much more likely that you’re surrounded by a bunch of critical busybodies who have said hurtful things that damaged your self esteem.
Keep your chin up (figuratively, not literally), and just keep being nice to people and being yourself. Getting to know people is hard for almost everyone. If you want to get more comfortable talking to people, you could take a debate class or a job or volunteer position dealing with the general public. Your face is soooooo not the problem, I bet it’s as beautiful as your personality. :)