Firstly tell your coach you are scared - or get a parent to tell the coach.
If one of my gymnasts tells me they are scared of a move, I have them go back to a progression they were comfortable with and then either they tell me when they are ready to move on or I tell them if I think they are just stalling!
On beam my progressions go like this
1) Do hundreds on a line - when competent, as in 10/10 in a row stick on the line, move on to no. 2
2) Put mats underneath the beam right up to the top so gymnast is practically on a floor beam (we don't have one at our gym) and put a pad on top of the beam - do 1 with support so I know exactly how competent the gymnast is - If I do too much supporting they go back to a line. If I do nothing, they have to stick 5 in a row on their own
3) Once number 2 is complete, take one mat out from under the beam - stick 5 in a row
4) Take the next mat out - stick 5 in a row - etc etc until no mats are left under the beam
5) put the mats back underneath and take the pad off the beam. Repeat stages 3 and 4
6) Stick 5 on high bare beam with no mats
I always support the first attempt
When my gymnasts reach stage 6, the skill becomes part of their warm up, so each session they have to stick 5 on high bare beam - I do this because I find that with the bwo in particular if I let them off doing them even for a week fear creeps in and we all go back a stage, so I'd prefer to spend some time doing them every session just to keep them going!
Perhaps you could have a think about which of those stages you would be comfortable with and ask your coach if you can just do a few at that level first, then build your way back up to the high beam? If you go in with an idea of what would help your coach might be willing to let you try. You might just need to do a couple with support to build your confidence up again!
Most coaches are reasonable, but I have read of a few instances where the gymnast says the coach won't let them revert back a stage - however I would personally rather have a gymnast spend 10 mins working at a level they are happy with, then get on the high beam and do the skill, rather than have them stand on the high beam crying or just not going for a skill! There is nothing worse!
Sorry I've gone on a bit!
Good Luck!