There are several ways to stop recording on the Dubb Chrome Extension.
Hit the Dubb Chrome Extension icon in your Chrome Browser
2. Hit the native STOP button in Chrome
3. For PC: Tap ALT + C to cancel and discard the recording.
Tap Alt + U to upload the recording
For Mac: Tap Option + U to upload the video to your Dubb account
Tap Option + C to cancel and discard the recording
Here is a video with full instructions: