you didn't have a 90 day visa. You had 60 days and extended it so the stamp tells you what day you had to leave by. Ramifications of overstaying? Example: You get stopped for some reason, status is checked and you're on overstay. Then, worse case scenario, could be taken to airport and made to buy ticket and leave, fined, banned. You might get away with it but it's obvious it would be an overstay you could have avoided. Or. . they might just tell you to pay overstay on exit. 🤷