Hello I starting using the trial version on Nov18th, still have plenty of time to finish the trial.
You can remove the registry value HKCU\Software\actionstitch.com\ActionStitch\License
and restart ActionStitch (right click the system tray icon and select Quit). After restarting ActionStitch, if the windows title says Trial Edition then it should be all good.
For macOS, run this command in Terminal:
defaults delete ~/Library/Preferences/com.actionstitch.ActionStitch.plist license