Hi Geki and welcome to subsim
You can adjust the error for nav fixes in your TDWoptions.py using the options editor.
For why your fix was so far off
The dead rec fix applies a % error from your last fix. If you do many dead rec fixes in a row - then this error will be increased. Try and use a celest fix now and then to help reduce dead rec errors.
You could also try the real nav script (check my sig for mod downloads) - it will take fixes at set times, mixing both dead rec and celst.
