No first hand knowledge but a couple of ideas -
Did you check with guest services to see if they might give you some cash against the credit card on file for your account?
Or, in doing a quick search - when you get off the pier, turn left and walk about one & a half blocks, past Calle 7. On the right there is a hotel, Casa Mexicana. It says there is a Scotiabank ATM location in the hotel. It comes up as ScotiaBank ATM 7-Eleven, open 24 hours. They have Global Alliance ATMs with several banks around the world including Bank of America in the US.
In the event you csn see this pic, it shows as 5 minutes walk from the middle of the pier so maybe 10 or so from the Magic?
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I have no personal experience using them in Mexico but have in other countries. Seems like it would be a safe one to use if needed.
Good luck!