AFE4300: How to improve data value?

Hey, I use AFE4300 to measure BCM.

I test it with RC series, with 464Ohms and 105.6 nF

My value have different % of error, sometimes it's about 0.02% sometimes 1.xx% sometime 20.xx% in FWR mode

I haven't added the resistance of wires and breadboard, but, for example, 1 wire has 0.3 Ohms of resistance 6*0.3 = 1.8 Ohms the full resistance of wires + ~ 1 Ohms (for example) the resistance of breadboard

How to improve to get less then 2% of errors

And the second question, do I need to calibrate the system every time when I measure in the same session, or after reboot/reset. I mean, I powered my board and calibrated once, after that I gonna measure in single/continious mode BCM, do I need to calibrate again before measure?

My code is

uint16_t FWR_read(uint32_t input_mask, uint8_t freq, uint8_t delay)
{
	set_frequency(freq, false);
        nrf_drv_gpiote_in_event_enable(DRDY_PIN, true); // enable pin IRQ
	write_register(VSENSE_MUX, input_mask); //Select VSENSE RN1-RP0
	write_register(ISW_MUX, input_mask);	//Select IOUT RN1-RP0

        nrf_delay_ms(delay*1000);
        uint16_t result;
        while (true)
        {
             if (dflag == 1) // when IRQ pin is changed from high to low dflag becomes 1
             {
                  dflag = 0;
                  result = read_register(ADC_DATA_RESULT);//*(1.7/32768.0);
                  result = (result >= 32768) ? result - 65536 : result;
                  break;
             }
        }
        return result;
}

void set_frequency(uint8_t freq, bool set_IQ_demod)
{
       write_register(BCM_DAC_FREQ, freq);
}
  afe4300_reset();
  nrf_delay_ms(100);
  write_register(ADC_CONTROL_REGISTER1, 0x4130); //Differential measurement mode, 32 SPS
  write_register(MISC_REGISTER1, 0x0000);
  write_register(MISC_REGISTER2, 0xFFFF);
  write_register(DEVICE_CONTROL1, 0x0006); //Power up BCM signal chain
  write_register(ISW_MUX, 0x0408);
  write_register(VSENSE_MUX, 0x0408);
  write_register(IQ_MODE_ENABLE, 0x0000);
  write_register(WEIGHT_SCALE_CONTROL, 0x0000);
  write_register(BCM_DAC_FREQ, 0x0032); //0x0040
  write_register(DEVICE_CONTROL2, 0x0000);
  write_register(ADC_CONTROL_REGISTER2, 0x0063); //ADC selects output of BCM-I output
  write_register(MISC_REGISTER3, 0x0030);

  r1 = FWR_read(0x0201, 50, 0.5);
  r2 = FWR_read(0x0202, 50, 0.5);

  double slope = (Ry - Rx) / (r2 - r1);
  double offset = Rx - (slope * r1);

  uint16_t z_code = FWR_read(0x0408, 50, 0.5);

  double Z = slope * z_code + offset;
  double Z_comp = sqrt(pow(RC_R, 2) + (1 / pow((2 * PI * (50 * 1000) * RC_C),2)));
  double err = 100 - Z * 100 / Z_comp;