How do I backfill my plant?

i'd start with a gently placed / gently packed mound around it roughly as high as you want to go... this will help protect it if a clump of substrate rolls toward it... big enough mound to protect it as you fumble around in the pot (your or me.. you-plural :P ) then, just carefully fill in and tap down softly to even it all out. when you water, it'll pack it down further. May need to add a bit more than you expect.