I’m not sure why everyone is saying that ECs don’t matter to a major. They don’t always have to align for an applicant to be successful - I certainly agree that there are national FBLA winners who major in a science, lots of kids who have jobs and sports that have nothing to do with any major, etc. But demonstrating genuine interest in a major through an EC can certainly be helpful for most majors, including (and perhaps especially) ones like computer science.
I would recommend including your Roblox games in your activities list. Very few AOs would ever take the time to look up the actual games to gauge traction, so you are unlikely to be dinged for them not being big hits. By including it in your activities list, you are able to show how much time you spent (sounds like it was significant). Also, going back to the AOs not having time to look up stuff like this, there is no pressing need to include your user name. Instead, use the limited space to briefly explain the games in an interesting way.
This approach is usually more effective than talking about the game creation in a supplemental essay, unless there is something unusual or compelling about your process.