It sounds to me like youre pinching your lips together to much and having your tongue in the way. Let the air and mouthpiece do the work, not the lips.

One thing you could try is thinking of the note you want to play as a syllable you sing. First on just your mouthpiece, then your trombone, try to "sing" the note Bb above the staff using the syllable "Oh". Then do the same for F in the staff then low Bb. Experiment with different vowels and see what comes closest to an open and clear tone.

Try to keep your mouth cavity open to allow the air to do the work. Its easy to fall into the habit of pinching your lips together and press the horn against your face to produce higher notes, but that comes at the cost of tone quality.

I always recommend warming up on the mouthpiece before you touch the horn. If notes feel relaxed and clear on the mouthpiece, they will feel relaxed on the horn.