pg's "Keep your identity small" comes to mind. But when it's a description of your mental status, it seems less like a label you choose and more like a label that chooses you.
In particular, it's different from wanting a smaller belly or bigger muscles or more money. All of those things are mutable. But being an introvert seems like a fundamental fact of your existence that's unlikely to change. In that context, isn't it better to wear it on your sleeve?
It's hard, certainly. But that's where a sense of community can help.