I really want to take ap lang next year so I can become a better writer, but I am worried because I am not the best essay writer under timed conditions. I can do well on take home essays though. What I want to know is if there are assignments other than timed writings to help your grade in the class, such as classwork, projects, and quizzes. If so, can they balance out essay grades.
It depends on who is teaching it. The AP EL&C course leaves a lot of room for interpretation for teachers. My teacher does a good job giving us lots of (easy) homework/reading/analyses, and doesn’t totally immolate your grade on timed essays.
You’ll be good at writing timed essays by the end of the year. That’s the point of the class. No one goes into it and is fantastic at writing that quickly, economically, and succinctly. 
I’d go for it. If you’re still not convinced, it’s an extra AP. And you’ll be writing essays in any normal Honors English class; the only difference will be you will practice timed essays in Lang.