UDisc uses the same mechanism as Google Maps and other apps to get your location. An estimate of accuracy is always displayed in the lower right corner, but this number is not as useful as simply using the blue dot on the screen as a guide. If the dot is accurate, the reading will be accurate.
I can see that the blue dot is where I am standing, so I don't worry about the ± 39 ft. I know the reading will be accurate anyway.
UDisc tells me when it is very confident in its reading, which is useful if I'm in an open field and unable to rely on the blue dot.
If you are not getting as accurate a reading as you'd like, it is probably because of interference between your phone and GPS satellites. There are several steps you can take to improve the accuracy of your phone's GPS signal.
Avoid being under cover. Anything between you and the sky can affect the GPS reading, including trees, leaves, and buildings. Accuracy improves based on the number of visible GPS satellites, so the more horizon and sky you can see, the better.
Ensure that your phone is set to the correct date, time, and time zone.
If the signal is way off, restart your phone.
Make sure you have at least a cellular connection. Wifi is even better, but unlikely to be found on disc golf courses.