Please hold the horn with your right thumb on the outside of the valve casings, right between the first and second valve. This with do wonders for your posture and protect you from possibly straining your hand. If you ever have to play faster phrases, this will also make it much easier. When doing this, you want to open your hand up as if it were a claw opened up in a claw machine. If this imagery doesn’t help, imagine that your holding a tennis ball in your right hand while playing. Hope this helps!