> Sometimes I can hear you saying A and PA and sometimes O and PO
'a' is just reduction of sound due to fast and fluent speech. If you talk slowly/meditatively this sound shifts a little to 'o', but never gets as sharp and clear as stressed 'o'.
There are two accents in Russia: 'окающий' and 'акающий' ones. 'акающий' is more common.
https://ru.wikipedia.org/wiki/%D0%9E...BD%D1%8C%D0%B5
So, technically you cannot be wrong, you just get accent (imho, countrylike one).