Try going to this path "C:\Users\<your username>\AppData\Roaming\Godot\app_userdata\Simple Marble Race" and deleting the file "race-autosave.cfg", then try opening the game. If that doesn't work, delete the "settings.cfg" file, although you'll lose your progress. But if that fixes it, you can edit the new settings file with Notepad and change the "coins" value so you can buy everything again.