I haven't used it in C2 yet, its on my todo list
Your using RegexMatchCount which is a count method, so with the example, it should return int 3.
If that doesn't work can u try using "@www\.(.*)\.com@"? Not sure if C2 needs the delimiters, in this case i am using "@" just to keep it simple, i won't go too much into it
Note: RegexMatchAt and RegexReplace would be more useful than RegexMatchCount
With RegexMatchAt, it only would return one result so you should do each website one at a time. For example, a list of website urls in a loop
One last thing i forgot in my last post is the brackets (). inside is what you want to capture. so if you had "www.google.com" with regex pattern "www\.(.*\.com)" RegexMatchAt will return "google.com"