You're taking about the Compass app on AW? It has a backtrack feature, which must be useful. But your challenge seems to be the "final 20 yards". For me, when I'm away from my car for a long period, I take photographs and make notes of the exact location. If it's a proper parking lot it will have level numbers and parking spot numbers. If it's a field event then it's tricker, but knowing the cars around you (though some may be gone) can provide a good point of reference.
You didn’t provide relevant information to determine which sort of scenario this is.
AirTags rely on the Find My network, which relies on iPhone users. Compass relies on magnet north and I believe GPS.
If it's a Wifi Airpad it's likely not more accurate than AirTag, though the sampling frequency may make one appear more accurate than another. So next time you might find the AirTag is closer than the iPad. Though with an iPad with Cellular I imagine that's the best solution. But not for me.
All the same, I think that making notes and/or photos of where you park is your best bet. AirTag/iPad as secondary.
I do use the Compass app regularly on hikes, but obviously I'm never heading back to 5,000 parked cars.
Next time you’re out in a similar situation then set a waypoint on the compass app for your car. Try to navigate back without using the waypoint, and see which is better. You’ll see that it depends on the environment. Multistory parking lots are much different to open fields.