If your rendering is under- or overexposed, this may be caused by:
1. Wrong exposure parameters
To fix this, depending on the workflow you are using, change exposure parameters either in Corona VFB's "ColorMap" tab, current camera settings or in Render Setup > Scene > Camera/Exposure/Tone Mapping.
See: Can I change exposure during rendering?
See: How to use photographic exposure controls?
2. Wrong lighting
Make sure you are using proper light units and intensity and that your lights are facing the right direction.
See: What light units does Corona use?
3. Wrong materials
Make sure your materials are not too bright or too dark.