When I am in my school band room with the members of the jazz band or concert band, I can play great. Everything is east and flowing. But when I go home and try to play, I can barely get to the G on top of the staff and my articulation is very sloppy. This also happens during my lessons. I have an audition coming up and it is really scaring me because at this rate I can't even play my piece all the way through. I assume that it's some kind of stress and I need to relax but I don't know how to do so. Can someone give some advice?

Hey! Most people find it easier to play in unison because the sound of the section makes up for the sound of your own horn whether it sounds good of bad. When you're playing, you get this adrenaline rush that excites you only when you're playing in a group. When you practice, try this. Play along with a song. You could find your piece probably on YouTube. You'll notice how well you play. When you practice, you tend to bore yourself. The trick is, love your horn, love the mistakes you make and play with that same excitement. With practice, you will play even better!

You might find this helpful...

http://www.thetrumpetblog.com/controlling-your-nerves-part-2/

I know this is way too late of a reply, but it sounds as if you're becoming very self-critical when you play alone, but when playing in an ensemble you tend to focus on your sound fitting in the ensemble/section/etc. When performing or practicing, it's important to "let it go" when playing. The only thing that you should be thinking about is the sound that you want to recreate and use the trumpet as an extension of the sound in your head. When you start to think about your fingers or how you blow to create a nice tone, your range and tone suffers. I know this is a rather unorthodox way of thinking about music-making, but it is the next closest way of explaining how to develop "effortless mastery".

Unfortunately, nobody, not even me, can teach you how to do it. It is a process of trial-and-error and having your body correct itself to the point that it can recreate that sound you have in your conscience and then do it almost unconsciously. Try this sometime in your practice sessions. As Arnold Jacobs would say: "focus on the beauty of the sound".

Good luck!