Fitness App not tracking steps correctly

If the Fitness app is undercounting steps, check:

• Settings -> Privacy & Security ->Motion & Fitness and make sure Fitness Tracking is ON.
• Health -> Steps -> Data Sources & Access and confirm your Apple Watch/iPhone is listed.
• Restart both the iPhone and Apple Watch.

If it’s still inaccurate, try a 20-minute Outdoor Walk to recalibrate the Watch.

More Info: Apple calibration instructions

It may be worth sending Apple feedback about this. try here: Feedback - Watch - Apple