Wawa,
thanks for pointing in right direction. I taught that 10 bit resolution is enough for this project and that commercially available (but cheap) amplifier is good solution. First asumption was very wrong, second one only wrong.
I have made new wiring with HX711 and except solving problem with bad wiring (99% this was the problem), measuring is now with error that can fit to normal distribution.
Thanks once again.
Zoran