Why can't I see the calculator while editing?
Squarespace stops custom scripts from running inside the editor so a faulty script can't break the editing screen. The Code Block therefore shows a placeholder or nothing at all. That's expected. Save, leave the editor and load the public page — that is where the calculator renders and where you should test it.
If the public page is also blank, the most likely cause is a plan that doesn't run JavaScript in Code Blocks. A direct link to the calculator works on any plan as a fallback.