Sorce, you cut what, 2/3 of the rootball at least, if you snuck a few handfuls of bonsai soil in there? 3/4? What’s your aftercare like?
I just repotted my nursery blue (bought last June, nothing done to it), but sort of chickened out. I sawed the bottom one-third of the rootball (Lord Mugo style), made the sides of the rootball fuzzy (tons of white feeder roots like yours), but then I selected a big pot, just a bit shorter than the nursery can, but a fair bit wider (my first option was a cut off nursery container, but to squeeze the tree in I would’ve needed to remove a fair bit of roots around the perimeter).
I guess I took the slow, slow road. At least, if the tree survives, the trunk is going to thicken for sure. You took the highway... either to bonsai paradise, or hell!