Hey there, I had the same problem, and maybe you are missing one step from the install instructions:
How to use:
OBS Virtualcam has two main methods for outputting video from OBS. The first is the Preview output, which is enabled from the Tools menu. This output will provide exactly what you see in the Preview in OBS, including any changes or scenes you might switch to. This is the most common method, and probably what you would want to use.
Preview Output:
1. Select Tools -> VirtualCam in the main OBS Studio window
2. Press the Start button, then close the dialog
3. Open your program (Zoom, Hangouts, Skype, etc.) and choose OBS-Camera as your webcam.
Gretting!