With practice, you'll get this down - I promise you.
Remember, if you're new to any move like this, you're asking your fingers and hand muscles to move into positions that they're simply not used to.
As with every jointed part of your body, it's going to take time to 'train' the muscles and ligaments involved to do what you want them to.
You wouldn't expect to be able to pull off even an intermediate Yoga position within a couple of hours, would you? Believe me, this is ABSOLUTELY no different!
In short - persevere -
stick with the pratice for a couple of hours a day (in bursts of 15-20 minutes max) FOR A WHOLE WEEK.
You may think this is over-kill, for something that, on paper, looks as though you should be able to perfect within minutes, but this is often where authors who teach stuff like this fall down (yup, even in RRTCM!

): They FAIL to tell you that even the simplist of moves require
significant effort to learn.
Please - don't look for short-cuts, hints, tips, or anything that purports to make the move 'easier'; they either won't work at all, or will lessen the final appearance of the sleight.
Work at it for a week, as I've suggested, and then come back to this thread, and let us know how you're progressing?
Want evidence that what I'm saying is correct? Talk to anybody who's bought a De'Vo DVD, with the impression that, say, Cradle to the Grave or the Cobra cut will be attainable within a day or two!!
Hope this helps!
Rob