most mustangs have the same bolt pattern of 5x114.3. I think it’s been the same since 1994. Your bolt pattern for your GT350 is 5x114.3 also.
Man, that sucks.
Not that it helps you now, but I bought a compact spare kit from 2007-2024 Ford Mustang GT Performance Package Spare Tire Kit
Look at the Fakebook gt350 parts group for a local guy selling a set. Maybe he'll let you borrow/buy 1?