Got for it - you use JS in order to manipulate the DOM - so knowing HTML is important, but once you are over the basics, you can give it a shot. Another thing to take into account is that JS goes far beyond manipulating the DOM, you can use it on the server(NODE JS) and there are several front end frameworks out there that you will encounter. Is easy to get overwhelmed, so it is important to define the scope of what you want to learn first.
The worst that can happen is that you have to go back and do the HTML/CSS sections again. I might suggest skipping to the Tribute Page build, which can easily be done without JS. If you can manage that, then you’re probably OK. None of us have every little thing about HTML and CSS memorized. It’s more important that you know the basics and know how find what you need.
The only thing I’d check is that you know some layout framework. FCC uses Bootstrap, but you’ll want at least some kind of a grid system for some of the projects.