(Oops! My first reply wasn't very useful because I confused @BinhQuang with the OP...)
Do you have franzliedke/studio set up, or a Composer path repository? In order for the root Composer installation to know about your extension's autoloading rules, you'll need to get one of them working.
Davis Also, my version doesn't show up inside the admin panel.
The versions displayed in the admin panel reflect the package version that has been installed via Composer/Packagist. No version is displayed for in-development extensions.