I'm a senior at UC-San Diego and my pre-med advisor said that UCLA takes letters of interest with a grain of salt. It's much more important for you to write them a letter of update about what you did last semester and intend to do this upcoming semester to show that that you are an "active candidate," and have been doing more than sitting on the couch since you applied. I'm also hoping to spend the next four years of my life in LA so good luck!