Is AP English Language and Composition worth taking?

I'm going to be a Junior this coming school year. I signed up for AP English 3. I have to read The Scarlet Letter for the summer ignment and write an argumentative essay and yze pages. I was starting to read the book and I'm REALLY just overwhelmed! There are so many words I don't know! This got me worried so much because I feel like this is a mistake to take this cl since this book is kinda hard to understand but it's just the difficult vocabulary. I'm worried about the timed essays also. I've never even yzed a book. I'm really worried. I do like English it's just that my vocabulary isn't as high as a top college student.