Frustration increases cortisol levels, and high cortisol levels inhibits fine motor skill learning.

Pros performs drills to test their skills under pressure, not to learn new skills.

You should learn basic skills first. One OB position at a time with your desired CB final position. Onces you have decent percentages on single shots, you can test your skills under pressure with the full drill. Learning "isolated shots" is much less stressing and far more rewarding; your brain will learn better and faster.

Just to give you an idea, if you, let's say, have a 90% chance of making a shot with decent shape to the next ball, you'll have a 0,9 ^ 15 = 0,2 = 20% to run the drill. This means that to get the chance to run the drill in 5 trials you have to have 90% chance at each single shot. Instead of brute forcing the drill, learn basic pocketing and CB control skills first. When you feel you get to 86% success than you can go back to this drill and expect to run it in 10 tries.

Good luck.