I'm new to Stack Exchange, and my main user only has 16+ rep. And it's been blocked in Code Review. I need to use Code Review today. Should I use an alternate account?
Judge yourself: do moderators block you so as you would have to create a new account? It does make no sense. The block is supposed to be an "emergency break" (don't speed ;)). You should at least look around you and try to find the reason for it.
If there were some problems with your posts, you might want to post more carefully now, trying to provide less content of not really good quality, and not immediately removing downvoted posts (but fixing them!), because this will contribute to another ban pretty fast.
But trying to create another account is dishonest (and illegal - you won't succeed with using Code Review by spawning new accounts anyway - this will be detected). Yes, you need to use Code Review today, but you probably didn't follow the rules while using it before? Then it's time to do that, though - with your existing account.