When you take pen 3000 and go to castle to write a paper,game crashed (((
It looks like your save is corrupted, so I'll send you a save file just after that mini-game instead. Here's how to access your playdate, like a USB: https://help.play.date/games/backups/
Next, please locate the "Data" folder, go inside it and find another folder that should look like this: "user.*****.com.mateuszmichalak.thefallofmagiccastle"
There should be 3 files in there (I'd be very happy if you zip them and send them back to me, so I can investigate further).
Here is a save file, just after winning the mini-game: https://drive.google.com/file/d/1XD25qeVIx3lFTTT-fHiC31ScgAbgWcSb/view?usp=share...
Inside you've got 3 files (new save) that you need to copy into that folder I've mentioned before AND overwrite the ones that already are there (old save). Now you should be able to continue :)