hair isn't quite platinum... help!

hi guys... first time poster and i need some help!

my natural color is a dark brown and last tonight & today i used a store-bought bleach and a purple toner in an attempt to lighten to platinum blonde again.

now, my hair is pretty damn blonde, i'd say maybe a shade or two darker than platinum, with a goldish tone to it, though the purple toner took a lot of that out. i want to lighten to platinum, but i'm not sure how best to do it. it seems like the purple toner i got (clairol) didn't really help too much (used it with a 20 V developer). it took a lot of the brassiness and yellow out, but it still has a light gold hue and is not nearly a whitish/platinum yet.

i have another permanent haircolor i purchased from loreal technique called "preference mega blondes" in "lightest ivory blonde" shade with a blue and gold base. would it make sense to use this with the corresponding developer to lighten my hair to a finally platinum shade, or should i try something else? i'd appreciate any tips!!!