Well 1st off you selected a procumbens with an exceptional amount of juvenile growth.
Personally I think juvenile growth has less surface area for sunlight. It's an assumption for me.
Truth is, it was stressed at some point prior to your purchase...now it's insulted double duty.
A junipers strength comes from its foliage, which will help speed recovery after repotting or
collectively gain vigor prior to a work out, rather than going from surgery to physical therapy in same day/season.
You're going at this like a JM in Spring at bud brake though, unpotting and a harsh cut back
with more than half of the remaining foliage being juvenile at that.
With it unpotted, what did you do with the feet this go around?
You could do 1 of 2 things here for a successful beginning.
Please allow me to illustrate...
Work the foliage
or, work the roots
Hope this helps your endeavour into the horticultural facet of conifers.