I have seen this happen before, where the first thing I would try is temporary unplug the power to your NOW Stick and Router.
I have seen reports it might take a day or two for the Watchlist to reappear automatically on people's account.
Can you see your Watchlist when logged into the NOW website under My TV?
Try the power down on the Stick and Router first.
If that doesn't help, try some of the trouble shooting steps in this linked guide.