The complication is not updating
The complication should update every 15 - 30 minutes (and more frequently -- every 5 minutes -- if the Cardiogram app is open in the background on the iPhone).
If this is not happening, try restarting your watch. To do this, hold the side button for a few seconds (not the digital crown), and slide the power off button on screen-this will turn off the watch. To start it again, click the side button. Once the watch is restarted, sometimes that would fix the complication issues.