Firstly, well done for looking for work. Please don't put yourself down, try to think positive. If you go into an interview with the attitude that you are to fat to work, the interviewer will pick it up. You should be thinking, I am curvey, classy, confident and ready for this job!
Make sure your resume is up to date and full of all your experience etc. Make getting ready for the job interview like a pamper session, as if you are going out with some friends. I am sure you have some clothes that look good on you. Pants and a nice blouse are always good, sensible shoes. Do you have a suit?
Be confident and clear when you speak, ask questions and do mock interviews with your friends to practse so that you are brimming with confidence when you go to the interview.