There's no guarantee the Wayback crawled your site at any given time or has a copy of the content. This may be for a few reasons:
The Wayback Machine just have never learned about the existence of your website, and therefore didn't know to crawl it.
The content it archived may be out of date, not reflecting any updates you made after it was archived.
You may have instructed, through the robots.txt file, not to crawl your website.
Another risk is that the Wayback Machine website itself is notoriously slow, so attempts to recover content there can be painstaking and time-consuming.
Do not rely on this as a backup strategy. It's truly a last-ditch effort, and should be used only to either quickly retrieve a small amount of lost content or as the final item in a backup recovery checklist.