The ADC is 10 bit, the largest value you can read is 1023 (10 1's). BTW check to table in the ADC section re. recommended ADC clock source, at 8 Mhz use Fosc/16 or Fosc/32. See note re using FRC as a clock source above 1Mhz.

You seem to have missed out the conversion to 0v1.

George