Patchy blonde dye job. What to do?

My hair is naturally a dark ash/dirty dishwater blonde color and I decided to buy 2 boxes of the L'Oreal Paris Absolute Platinum box dye to lighten my hair with. I've only ever gotten blonde highlights from the salon, but it's getting expensive so I made the decision to try this from home.

It worked good on my hair. The color is light. It's kind of a buttery yellow on top where my natural hair color was and it's a bit brassy in places, but I have Shimmer Lights shampoo and conditioner to help with that. The only problem I ran into is that it was unevenly applied in places. It was completely my fault. I had more than enough dye to go around, but I didn't buy a brush to apply it with and I had to do it with my fingers and hands. The bleaching powder makes the mixture a little gritty and hard to move around. Needless to say, I have some horizontal striping in areas and some patches on the back and sides of my head that were either missed or didn't have enough dye on it to process correctly. It looks kind of bad. It's definitely noticeable. I was wondering what I could do to fix this.

I died my hair on Thursday December 31 and was going to wait until Thursday January 7 to try to fix this. My hair has always been very healthy and this dye is ammonia free with very little bleach involved. I figured a week was a good amount of time to wait since my hair still feels very soft and healthy. I use Moroccan Oil after every shower, conditioner, and heat protectant spray.

Do I buy more boxes of the Absolute Platinum hair dye and put it in the darker areas first and then do the rest of my head, do I just apply it to the dark areas, or do I apply it all over as if I'm doing this for the first time again? I definitely want to go lighter since it's not as blonde as I wanted it to be, so I was planning on dying it again soon anyway with this same dye.

Thanks!