My watch is updated

From the article: Take an ECG with the ECG app on Apple Watch - Apple Support

How to get the best results

1. Rest your arms on a table or in your lap while you take a recording. Try to relax and not move too much.
2. Make sure that your Apple Watch isn’t loose on your wrist. The band should be snug, and the back of your Apple Watch needs to be touching your wrist. 
3. Make sure that your wrist and your Apple Watch are clean and dry. 
4. Make sure that your Apple Watch is on the wrist that you selected in the Apple Watch app. To check, open the Apple Watch app, tap the My Watch tab, then go to General > Watch Orientation.
5. Move away from any electronics that are plugged into an outlet to avoid electrical interference.

A small percentage of people may have certain physiological conditions preventing the creation of enough signal to produce a good recording — for example, the positioning of the heart in the chest can change the electrical signal levels, which could impact the ECG app’s ability to obtain a measurement.

Liquid-free contact is required for the ECG app to work properly. Use of the ECG app may be impacted if the Apple Watch and/or skin aren't entirely dry. Make sure that your wrist and hands are thoroughly dry before attempting a reading. To ensure the best reading after swimming, showering, heavy perspiration, or washing your hands, clean and dry your Apple Watch. It may take up to one hour for your Apple Watch to completely dry.