Putting on my mean face

As a new teacher I am trying to learn about all of the tricks of the trade. One of the biggies for this profession is classroom management. It is constantly discussed and is always a matter of concern. I get the impression that it is nearly more important than any content I will teach. However, one thing about me... I'm nice. I'm not a person with a loud voice or firm personality. I am not an older man my dad's age (like my cooperating teacher) and I'm always friendly. So while I am getting in front of these kids I keep getting asked by the CT about my previous experiences and told that I need to be sure to be firm so I don't have a problem in the future. So far the kids are mostly great to deal with (and certainly way better than my last placement). So I'm wondering... do I have to be a loud, firm yeller to be a good teacher? Do I need to look mean and scary or like their dad? If that is the case I will not be acceptable - because that is simply not me. I am definitely firm and to the point with the students. I do not pal around and I do call on many of them and keep them to task. I just want to maintain my own personality in this. I will work to be better and better at managing the class - but I don't feel that authority has to be equal to the level of "firmness" I have.

That being said... today I was tested. A kid in the second period who tends to be troubling was defiant. We had a substitute and so I was in control all day. The kid refused to do a problem and was reading a book. I told him twice and the took the book. He said "I don't know it!" and pushed his papers on the floor, looking at me with disgust. He was not completely disruptive to the class. So I gave him my meanest look and asked if he would like to be sent to the office immediately. The sullen slump of his shoulders was so irritating. So I finished going over the work I was doing and put in the video we were to watch for the last few minutes of class. I then had him come with me into the hall where I had a discussion with him about his unacceptable behavior and how he simple could not behave that way again. I did not yell, but I was very stern with him and very serious - because this is a serious issue. He tried to make excuses and ended up with his head down and promised not to behave that way again. All in all I feel like I handled it well, I didn't lose my cool and I will maintain my own firmness with him and the class.

I'm still wondering though... when I tell my CT tomorrow... if he will think I should have been more firm?