Permesso di sigorno

Hi dears
I'm in a difficult condition please guide me or help me in this situation.
my visa is valid until 26 december but I made a mistake and reserved flight to 28 December. it is about 5-month I am in Florence but unfortunately, it takes a long time to go to fingerprint and get permesso, now I don't know what to do? my flight is transfer not direct to my home country. somebody says that they don't let you go out at the airport because you don't have a valid visa and also you don't have you permesso. if I want to change my flight it is so expensive. please guide me, if I don't change my flight they don't let me come back to my country?

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