Basically I am wondering if I go there as a Wiccan, will I be hanged
Just don't share your beliefs with the nosy old lady who might be living next door and attends the Mass every morning.
Wicca, as well as yoga and contraceptives, is on the RC's black list, still lots of people in Poland practise yoga, use contraceptives and some of them are even Wiccans. Don't worry, you'll be safe in Kraków, nobody's going to burn you at a stake, unless you want to befriend orthodox Catholic circles.