My watch keeps scrolling on its own . How do I fix it

You can try unpairing it and pairing again. Just make sure you do a back up first

Back up your Apple Watch - Apple Support

Unpair and erase your Apple Watch - Apple Support

Set up your Apple Watch - Apple Support

If none of this works, you will need to contact Apple @Get Support

From a web browser,sign in to iCloud.com with your Apple ID.

Go to Find iPhone.

Click All Devices at the top of the screen.

Click your Apple Watch.

Click Erase [device]. Select Next until the device is erased.

Click Remove from Account.

Then;

Set up and pair Apple Watch

Try this;