I'm sorry, I really wish I could fix this bug, it was definitely something with the save, but the game jam doesn't allow you to load more files... I'm really sorry! You can try to fix it just by searching in file explorer and deleting the save:
C:\Users\UserName\AppData\Roaming\Godot\app_userdata\Sparto School (change the UserName)
I'm not sure it will be located with this path, let me know if it doesn't. But I'm glad you liked it and thank you!