now you're talking lawyer stuff.

If the hiring company agreed in advance to pay you then they are undoubtedly obligated to pay what you asked. Of course they can always sue to get it back.

Whether you had 3 days or 3 months to design the site is a moot issue. You are the expert, not them. The site is badly designed and you should graciously offer to fix your work and not hand off a basketful of excuses.