Heart Month Challenge 2021

Be patient. It may take up to 9 days after completing the activity to earn the award. For more info, see the "Get help" section in:

Earn Activity awards using your Apple Watch - Apple Support

If you can't wait, sometimes restarting your watch & iPhone will speed-up the process.

How to restart your Apple Watch - Apple Support

Restart your iPhone - Apple Support

How do you know that "The special badges will show complete automatically when the activity is finished."?

I say again:

Be patient. It may take up to 9 days after completing the activity to earn the award. For more info, see the "Get help" section in:

Earn Activity awards using your Apple Watch - Apple Support

Restart your watch. It should do it.