How do I validate if the ADC data output I am getting is correct or not?
In your ADC initialisation, change this line

ADCON1bits.ADFM = 0;


to this

ADCON1bits.ADFM = 1;


As the datasheet explains on page 242

 

Your configuration effectively resulted in a number that was shifted 6 bits to the right, so was 64 times bigger than expected.

This is illustrated in the following figure from the same section of the datasheet: