I don't know how to start this off, but here goes:
I'm the lead trumpet player at my high school, and everyone always gives me postitive feedback on my tone. Whenever I play I sound great. But, I always feel a stream of air coming from the side of my lips. As hard as I try to close my lips, the air still comes out. When I looked in the mirror, I saw that one side of my lips were slightly opened when I played. It's very strange that I have a great tone and that I'm the loudest player in the band while still having a controlled sound. I'm worried that I might have to switch my embouchure and start from the beggining again. can anyone help me?

-sorry for the errors!

Try pulling back your corners. If that doesn't work you might want to consider a new mouthpiece. What size are you playing on now?

Couple factors to get out of the way first are the structure of you mouth/teeth/lips. How flat are your front teeth? Is your bell straight out, or slightly up or down. I am a brass tester at a leading brass manufacturer, so that means I play all day long. I have found that after blowing through trombones for about 3 hours then switching back to trumpets I sometimes "leak" out the sides. That tells me that that part of my embochure is fatigued or not working properly. Always blow straight through the horn, envision your air making the turn down the tuner and smile. Buzzing is a good way to build up your chops, meaning just blowing into your mouthpiece, you will here a distinct tone difference when you blow straight through the mouthpiece and when the air is inhibited.
I could go one for hours but I would say try the buzzing and you will also increase your stamina and range....

That is all..!!

Couple factors to get out of the way first are the structure of you mouth/teeth/lips. How flat are your front teeth? Is your bell straight out, or slightly up or down. I am a brass tester at a leading brass manufacturer, so that means I play all day long. I have found that after blowing through trombones for about 3 hours then switching back to trumpets I sometimes "leak" out the sides. That tells me that that part of my embochure is fatigued or not working properly. Always blow straight through the horn, envision your air making the turn down the tuner and smile. Buzzing is a good way to build up your chops, meaning just blowing into your mouthpiece, you will here a distinct tone difference when you blow straight through the mouthpiece and when the air is inhibited.
I could go one for hours but I would say try the buzzing and you will also increase your stamina and range....

That is all..!!

you need to close the corners with ur cheek muscles. make sure ur sides are closed. u might wanna move to a larger rimmed mouthpiece too, that might help.