Hi april_8500,
The support article Track your sleep on Apple Watch and use Sleep on iPhone includes the following tips to improve the accuracy of this feature:
"Get more accurate results with your Apple Watch
If you paired your Apple Watch after completing Sleep setup, you can still turn on Track Sleep with Apple Watch. In the Watch app on your iPhone, tap the My Watch tab, then tap Sleep. Then tap Track Sleep with Apple Watch to turn on this setting. To get the most accurate results when wearing your watch to sleep:
- Turn on Charging Reminders. On your iPhone, open the Watch app and tap the My Watch tab, then tap Sleep. Tap Charging Reminders to turn on a reminder on your Apple Watch to charge before your Wind Down time. If your watch battery dies, it won't track your sleep data.
- Make sure that you're wearing your Apple Watch at a comfortable fit. If your watch is too loose, the accelerometer might register too much movement during your natural sleep."
Additionally, Track your sleep with Apple Watch sets the expectations for this feature as:
"Note: Apple Watch tracks your sleep based on the sleep schedule you create. Apple Watch can also track your sleep when your Sleep Focus starts. To receive sleep data from Apple Watch, it must track your sleep for at least four hours each night."
Based on that, you may need to adjust your sleep schedule or use the Sleep Focus to ensure the most accurate results for tracking.
Regards.