What I'd do:
Pile mats right up to the height of the beam. Work like this until you are 100% confident, then take one mat away. When you are 100% confident, take another away and so on. I think this is more effective than going back to the low beam. When I was doing them, I found it easy to go for it on the low beam, but not on the high beam, purely because I knew I was higher off the ground.
Have a coach spot you for the first one or two just to reassure you.
Don't rush, take your time. In my opinion beam is worth taking time over, especially when the skills start to get harder.
If it gets to the point where you know you can do it, yet you just won't go for it, imagine your beam routine, do the bit of dance which comes before the bhs and do it, then go for the bhs with support. Gradually have your coach move away from the beam