Multiple exercises not reflected in exercise ring

I have the series 2 Apple Watch and iPhone 7. Both have up-to-date software. When I workout, I usually walk on a treadmill for about 20 minutes and then use a rower for 20 minutes. Walking on the treadmill, I use the “indoor walk” on my watch. When I switch to the rower, I swipe right and hit the + button and then select the “rower” option. I keep my heart rate up (130-140bpm) and when I’m done, I swipe right again and select “End”. My problem is that I only get credit in my activity tracker exercise ring for the 20 minute walk and not the 20 minute row. Help! How do I fix this?