SaileNav,
If it works now, then no!
I though you were using the internal 1.2V reference, that's why I suggested the ADC_REF_1V2 option, if you want to use the usual 3.3V then either do nothing (as now) or use ADC_REF_3V3. I see now that the problem is that you were using the option "INTERNAL", which has no meaning in the ADC library. I'm looking into ways of avoiding those kinds of mistakes (enum class).
JBeale,
The error was using the 1.2V reference for ADC1 instead of the 3.3V default one.