In my experience, ballet teachers who tell you to be yourself are very rare. When you get a step wrong, most of the time they will tell you to watch another girl in the class and do it liker her, or that girl will be called up to the front of the studo to proudly demonstrate for the whole class. Everyone is then told to copy her. In general, it seems like most dancers learn by copying, rather than knowing when they are doing a step right or not.
When I first started studying with a private coach at 12, she was aghast at how little I knew about ballet steps and positions. She would quiz me about what croise, ecarte, or en face meant, or what the different arabesques were, and couldn't believe that I didn't really know. I was just used to copying what the teacher showed, or what the other dancers did. She called this "monkey see, monkey do" dancing, and proceeded to thoroughly reeducate me. The problem was that I had been looking up to the other girls in my class as the standards of perfection, instead of learning to appreciate my own dancing. It's so important to know your craft inside and out, so that you can really become an artist, not just a very good mimic.
However, we all have our idols. Mine is Sara Mearns, from NYCB. I wish I could dance like her--so full of attack and abandon, yet lyrical and and soft when she needs to be. Everyone has a dancer they admire and want, or try to emulate, but it's important not to lose confidence in knowing that your own dancing is worth emulating as well.