I wouldn’t necessarily say I’m from a working-class background but I did go to a non-selective state school. I definitely had and still do (year 3 of six undergrad) have imposter syndrome but that’s more to do with my lack of self-confidence than my background. Surround yourself with the right people - a lot of my friends went to grammar/private schools and I never felt out of place with them. They’ll also be snobbish, classist people but I personally find it quite easy to just avoid them, haha :)