Hi! I actually just had this same problem - the solution is to view hidden files in the folder. Command + Shift + . (period) makes the hidden files appear. Once you do this you'll be able to see which hidden files/folders are taking up the extra space. For me, the git folder was taking up a crazy amount of space so all I had to do was delete it.
Hopefully this works, good luck with your submission :)
Topic:
Developer Tools & Services
SubTopic:
Swift Playground
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