If you're in the final three, they're seriously considering you. I wouldn't worry about your size, if you're feeling insecure on the day it won't help, but it sounds to me like you've got a very good shot at the job.
In response to your question, I started my diet 'wanting' to lose weight, but in denial about 'needing' to. I plucked up the courage to weigh myself after two weeks, and was horrified to discover I was considered obese. But I think it was a good thing for me, because 'needing' to, has put me in a much more committed frame of mind.