So the universe is expanding, but galaxies and clusters aren't, relative to each other, because gravity is sufficient to keep them bound. Ok, got it.

Why did the universe continue to expand when it was incredibly dense and all matter in the universe now was essentially adjacent? Wouldn't there be incredible gravitational forces involved? Wouldn't the universe turn into a superbody?

I'm sure this is incorrect and it's a problem that's accounted for, I'm just struggling to get a search engine answer for this and I don't own any physics textbooks.