A video would really help for us to see what might be causing the problem.
I agree.
If your technique on the skills you fall on is sound (it's pretty obvious that if you have bad technique on a skill, you are likely to fall. For instance if you don't keep your hips straight on a jump, you are more likely to fall. Same thing if your back tuck is low, if you are not pushing through your shoulders in BWO, etc.), then a fall is often caused by a lack of body tension while landing / finishing the skill. After landing, you should stand tall, head up, abs and butt muscles squeezed.
If you fall on your turn a lot (I agree it's a hard skill), maybe check your turn technique ? Very common mistake on beam are : not staying tight during the turn, not keeping upper body straight (mainly leaning forward because of looking down), trying to put your foot on the beam before the turn is completed.
Buuut, if you do this in training and you mainly fall during competition, it might just be a nerve issue ? Do you do a lot of "pressure" routines before a meet ? For instance routines with your whole team watching you ?
I know I sometimes try to imagine that I am at a meet and that I absolutely have to make this routine. And believe it or not, it does stress me out and helps me recreate the feelings of being on beam at a meet. My coach also have us do some running / light cardio exercices to get our heart rate up to replicate meet feelings (I personnaly don't find it very efficient but I know some people like it).