I feel like people are staring at me? Every time that I'm in band class, I feel like people are staring at me and I get really tensed up and shake. I don't know what this could be.

I . I really like that dr. Kardener pointed out to you, how common it is for people to feel like all eyes are on them when performing. If you are anxious about how well you perform or about being judged, on thing you can do is to talk to your band teacher and get some reality feedback. Be frank, tell your band teacher how tensed up you get. Ask your band teacher how you are doing. If your band teacher gives you feed back that you are performing well, this tells you that alot of your anxiety is coming from inside you. If your band teacher points out any areas of weakness, you can use that information to work harder in those areas. I think it was great (and showed courage) that you wrote in with this question.
While . While what you describe may be associated with other more disconcerting conditions, the commonest cause is what called performance anxiety. It is not at all uncommon for people who are about to be called upon to perform and have concerns or questions if they will fail or otherwise not do well. Of course, what happens then is called fulfilling our own worst expectations. If we do not feel confident, we get anxious and concerned others see this, shaking and tension follow and what it leads to is just what our worst fears were. So, barring any other conditions that may be associated which would require a through examination, you may try what is called the 3c's: catch it; challenge it; change. For example, if you catch the initial concern "i will not play well" and challenge it with "wait, i've played this well before, " or "i've rehearsed it and know the piece well, " or "i know everyone else is also a bit nervous about performing and I am not the only one, " and so forth, you begin to challenge the initial presumption that you caught and with the challenge modified the impact of the initial concern so that the change can occur. Of course, should this exercise prove inadequate or despite its use you continue having difficulty it would be important to speak with your physician and obtain more direct help from that person or a psychotherapist. Rest assured, you are not alone if the symptom is related to performance and not otherwise affecting your life. About half of a professional orchestra acknowledge such symptoms as do very successful public speakers, and many, many actors.