Oh goodness. You got pretty far there!
Once you unlock Heroes, that's as far as I have gotten in coding the game. So you're not missing out on any content.
I am releasing a new build soon that changes the layout and progression somewhat, however it will also end after unlocking the Heroes again. Once that update is here on Itch, I'll be focusing on new content from there.
I really hope you've been enjoying the game so far and I hope you'll also enjoy the new build, along with future updates! :)