If all you can pick out is your destination and your departure point, you want to keep yourself on a line between them. If your destination is off your right bow and your departure point is over you left shoulder, you're probably doing all right. Finally, you can use ranges to gauge your forward progress. As you paddle up a channel, look for a range off to your side. This side range can tell you how much progress you are making against a current.
Forward progress is indicated by the near object falling behind the far landmark.
You may find that for the last 10 minutes, while you have been happily paddling along, you were actually proceeding backwards. In which case you may want to ferry to one side of the channel and paddle where the current is slower. They are a quick system to double check what you may already know from other sources. Currents can be deceiving, the water can be glassy smooth while you are being swept dangerously out to sea, or drifting down into a tidal rip. Unlike taking a hike, when you stop paddling, you don't necessarily stop moving.