Apple Watch 4 measuring incorrect distances

My Apple watch is measuring incorrect distances when running over and over again.

I run a running track that is measured at 3.2KM, and it measures it over and over again as 3.02-04KM.

I am running outdoors, with my phone, and my watch has cellular as well. I have recalibrated my watch, and reset fitness calibration data. That worked for one run, where it correctly measured the track at 6.4 KM's for two laps. But upon running again tonight, it was 320 metres out over that same distance.

That's 5% out, which is not acceptable in my view given I am running with my phone as well.

I love using my apple watch, and it connects perfectly with my Iphone and Airpods, but I bought it mainly for fitness tracking and I fear I may need to go for something else if it is this innaccurate.

Is there anyway I can fix the problem?