600 lines of code though? For the 4 years you said you've been working on it. That is less than a half a line a day. Since I have started game dev I have wrote an average of 25 lines a day, including days off. And I don't even do it full time.
I have used it as a game dev platform. You can try to submit it. Roblox has a negative connotation associated with it. You'll be in the bottom 100 games.