I'm totally freaking out right now, can't help shivering.
Nice thing I've done?
Testing while developing. Although still have to fix a bug the last minute.
Conforming to CustomPlaygroundQuickLookable, and using Xcode mark up language
Write responses to questions in local files, but keep the submission window open. Apple actually asked me to login after I clicked the submit button, and fill out all information again.
What did I mess up?
I have not yet tested it without network. It should be fine when it is offline, but who knows?
I didn't have time to thoroughly write the most important part -- describing my Swift playground. It should be about the features and technologies that I used, in 500 words or less. What I wrote is exactly what you are seeing in the README -- random stuff that comes out of my mind.
Making a lot of singletons. Now I have to go through playground to render a world model with Karel. not sure what is happening.
How can I improve?
Finish stuff earlier! Earlier! Earlier!
Write technologies I used before writing the actual software. Plan before action.