Don't obsess over being well-liked by all of the students. All of us want to be liked, but it is a mistake to try too hard to be liked by your class. Students want to feel safe and protected, and sometimes the only way for you to provide that type of environment is to act a bit authoritative. Students aren't going to like it when you attempt to modify their behavior. You have to maintain control of the classroom. You are the leader that needs to rein your students in. A few frowns should be expected when you're doing your job.