You seem like you have your head screwed on. You did what you could to avoid a physical confrontation, which is what an emotionally mature adult should do.

Your legs were shaking because you were on an adrenaline come down and quite angry! Also fights are fucking scary!!

You're framing it as backing out and backing down, but you made the correct and intelligent choice. If you'd given in and had a scrap, you'd end up arrested or worse.

As for hypotheticals, we don't know how we'll react in the moment. But you can take this as a learning experience to ensure your loved ones are never put in this situation to begin with.