The room takes its cue from you. Walk in like you belong and most people will just assume you do.

Groups run on signals, and most people are too busy checking their own standing to audit yours. Walk in uncertainly, apologising with your shoulders, and the room reads hesitation and responds to it; walk in as though you have a right to be there and the same room mostly agrees without examining the claim. Less about confidence than about which cue you supply.

Practise the physical part before you feel it. Head up, slower walk, pick a seat instead of hovering. The internal version tends to catch up with the posture.