Hi Grab Shiny, Thank you for taking the time to play our game!
For the shoes puzzle,the intention was to have the shelf in the library with the red book to match to the shoes shelf(books at the position of shoes, red book at the position of the key). Additionally, it might have been unclear, but leaving the piano itself will cause the game breaking bug.
Thank you for your feedback and we are glad you enjoyed it :)
Wate͎̝̦̮̮r͉͓̭͔̭p̙o͖̤u̯̝c̼̘̣̞h͕͉̹̮͈͉̦'s͇͉̥̰̝ ͕̣̥̹̙s̟̳l͈͇̎̔ͤͯ͂ͮ͋a̷̦̘̺͓ͦ̍ͣ̄̏̆͗v̥̼̻̈̾̓̈́͐̐ͭ͜e̺s͖̤̄͆͆̍ͮ̍̅͝.̘̥̼̲̯̻̋ͨ