If you never read the book, then the movie is fine. I personally did read the book 1 week before the movie came out and was honestly disappointed. I did appreciate some tiny details they included, but all in all I believe the book had a better /more full plot line and allowed for the characters storyline to develop more.
Its still worth the watch since its a good summer romance movie but hands down I thought the book was among the best I read and Sarah Dessen is an amazing author.