Hi. I am in a high school band class. I need help with high notes. They sound like dying cats. Also how to do vibrato? I have been playing for 2 1/2 years and I haven't been getting better. Just staying the same. Any suggestions? Thanks!

Here is a youtube video that can help with vibrato. I picked up a flute and within weeks had vibrato and don't have a clue how to tell anyone how to do what just came naturally. In the video she shows some exercises to develop it.
https://www.youtube.com/watch?v=IjPTG7xiYy8&t=194s

My unorthodox solution to high notes is to learn to play a brass instrument as a second instrument. I was a French Horn player who picked flute as a second instrument. The muscles in my flute embouchure are the same as used to play horn. That means I started out with an embouchure most flutists would take many years to develop. Everything came easy on flute because of the "heavy lifting" required to play horn.