Thanks for writing.

Here's what I suspect from the details you've provided:

Hearing air before note means the aperture is too big, period. The lips are not in position to buzz. This range, too (f to Bb), is so weird sometimes. I think some players are between a high set and low set in this register. Could that be you? If so, I've never seen anyone err on the side of "too loose" in the embouchure. It's always the opposite: too tight. This would stretch the lips, thus opening the aperture too wide, and might cause undue stress in the corners ("shaky" , trembling, corners). It also makes for nearly impossible slurs. So..........sounds like this might be you.

What to do, then?
Well, a very wise man once told me "everything works where it lives". That very wise man was Buddy Baker.
He meant that we shouldn't use any more "strength" than is absolutely necessary for the task at hand. Once you trust that AIR will support sound more than muscle, you'll see what he meant. So often, we are WAY too tight for the desired buzz of the lips.

After about 5 minutes of really good breathing (check out the routine on the website), I would practice in the mezzo forte range from low Bb to D above the staff. Half notes at mm=60. Let your face feel as natural as possible, just don't allow air between the cheeks and teeth. BLOW each pitch and feel the pitch on your breath. Sense that it is AIRFLOW supporting your tone. Blow faster, perhaps, than you are accustomed. But blow very steadily, like blowing a pinwheel. Feel the steady air stream flowing directly through the buzzing lips and straight down the throat of your mouthpiece. On every pitch feel this. If sound wobbles, boost air speed and sustain it.
No tilting the horn, feel equal upper and lower lip pressure. Blow straight, steady, and relatively quickly, but not more than mezzo forte. Nice, big inhales after every 2 notes.

Play this both ascending and descending, enjoying your best possible tone.
Then stop and do more breathing exercises. You've got to get air flow happening, so you're not so reliant on muscle to sustain your sound. That'll get rid of the shakes.

Try this every day for the next week or so and let me know what you discover, OK?

As for your fear of making mistakes.........life is all about mistakes and what we learn from them. Live a little. Take a chance. Make a mistake. Then figure out why it happened and work to remedy it. Making the same mistake again and again is really not forgivable. But mistakes are truly a sign of our humanity. Our humanity is what makes music so real to us.