Blondie, I wish you lots of luck in whatever you choose, but please know that even though the professional world of dancing can be very competitive, you don't have to be in that world to be able to dance. I, too, had a dance instructor that constantly nagged me to lose weight. That kind of talk made me feel very fat, and in time, I made that assumption come true by eating to deal with my depression. At the time, I was about 155 on a 5'10" frame...not fat by any normal standards. Eventually, I became 326 on a 5'11" frame. Don't let that happen to you, okay?
Remember that being healthy is more important than being rail thin. Truly.