Hi mikaela82,
It sounds like you and your cousin are not seeing the correct totals for the Apple Watch fitness challenge you just completed. We're glad you've joined us in Apple Support Communities, and we can provide some assistance.
First, please make sure each of you has updated your iPhone to iOS 14.4.1. Then restart your iPhone to refresh it and reestablish connection to the internet.
Once the iPhone is updated, its time to update your Apple Watch to watchOS 7.3.2. Restart your Apple Watch refresh it and sync the Activity data.
Here are some resources to help you with this:
Update your iPhone, iPad, or iPod touch
Update your Apple Watch
Share your Activity and compete with friends with your Apple Watch
If the issue persists after making these changes, reach out to Apple Support for more assistance with your Apple Watch.
We hope that helps with your question and take care!