MC Link pulls your activity data from the Health app that is pre-installed on all IPhone devices. If the data in your Health app does not match the data from the Apple Watch this is an issue you would have to address with the Apple support team as it would be an issue with how the watch is talking to the Health app.
To make sure that your Health is showing the correct data you can adjust the priority of the data sources the accepts data from. Instructions on how to do this can be found here: https://support.apple.com/en-us/HT204351
Prioritize data sources
Here's how to choose the sources that Health uses first:
- Open the Health app, then tap the Browse tab.
- Tap a category, then tap a subcategory.
- Scroll down, then tap Data Sources & Access.
- Tap Edit.
- Touch and hold the Change Order button next to a data source, then drag it up or down in the list.
- To turn off a data source so that it doesn't contribute any more data for that category, tap the checkmark next to the source.
- Tap Done.
If multiple sources contribute the same data type, then the data source at the top will take priority over other sources. Any new apps or devices that you add go to the top of the list automatically, above your iPhone or iPod touch.
An alternative option is to turn off the Fitness Tracking feature of your IPhone itself; this prevents the Health app from counting steps from the movement of your phone effectively limiting the health app to using your Apple Watch data only. The Fitness Tracking feature is found in your IPhones settings under Privacy->Motion & Fitness