Hello greigoree,
Thank you for using Apple Support Communities.
I understand that you are having an issue with the route depicted by your Apple Watch. This can happen when the Apple Watch is not getting a good GPS location. Take a look at this support article addressing how to improve GPS accuracy.
"Improve GPS accuracy
GPS accuracy depends on the number of visible GPS satellites. Locating all visible satellites can take several minutes, with accuracy gradually increasing over time. To improve GPS accuracy:
Make sure that you've set the date, time, and time zone correctly on the device in Settings > General > Date & Time. If possible, use Set Automatically.
Keep a clear view in several directions. Walls, vehicle roofs, tall buildings, mountains, and other obstructions can block line of sight to GPS satellites. When this happens, your device uses Wi-Fi or cellular networks to determine your position until the GPS satellites are visible again."
About privacy and Location Services in iOS and iPadOS - Apple Support
Best regards.