Files not in my Site showing up on SiteMaps with Error

How do I get Google SiteMaps to stop searching for files that do not
exist, and as a result, showing that there are errors on my site?

There are four URLs being shown by Google SiteMaps as having a 404
Error. Which makes sense on one-hand because these URLs do not exist
on my website, but the catch is that they never existed on my site nor
were they ever part of the sitemap file I submitted to Google.

I've double-checked my sitemap and all the files on my site numerous
times and the URLs that Google is saying are part of my site do not
exist on my server nor are they shown in my sitemap file.
Interestingly, some of the html files are files that are part of other
websites I own/manage. I double checked all the files on those sites
(including the sitemap files for those sites) and there is no situation
where I list any of those html files with URL that Google says they are
connected to. All of the html files are shown in connection with the
appropriate site. (I hope this is making sense.)

In essence, I don't know how these URLs were created by Google and I
don't know how to get Google to stop searching for them. I'm concerned
that the continuing errors will negatively impact my site ranking.

Do you have any suggestions?