I actually used to do the same, autocomplete just generated renderosity.com instead because that's what I used in the beginning. Looks like clearing the cache and then type www.renderosity.com it will just generate that instead in the future, so that's OK.

Maybe the change is intentional, it's said that it's bad for SEO to use both, but people usually expect URLs to work without www so it may be a bad idea in that respect. Looks though as if a redirect can solve the problem:

http://www.themezilla.com/should-you-use-www-in-your-url-or-not/

https://ithemes.com/2017/01/09/www-in-url-domain/