Hi ​@Omc7slowaf, the accuracy of gps mostly depends on the device rather than an app. Having said that, if you're using more tracking apps on the phone and Strava is only on the background, it may have insufficient data.
For better accuracy, you might want to use a watch (apple watch, garmin, coros or similar) for tracking.
And to fix the already recorded activity, open it on the Strava website, then in the menu on the left, tap the three dots, and then Correct Distance. That will recalculate the distance based on map data, and should produce more realistic distance & pace information (provided that the route on the map is somewhat accurate).