Right, in that case I'd be inclined to try the 100 Natural Pale blonde, or even the 87 Natural Ultra Light blonde (if you feel you need extra lift)
I know you feel you've wasted a box, but its a nice "safety measure" to have at home in case you ever have a "disaster" and are too embarrased to leave the house - at least you know it is pretty close to your natural colour, tonally and in darkness.
You will need to do a strand test on new hair, not the hair you have already coloured during your first strand test, because you are going lighter and you need to know how it will react on virgin hair. So you need to sacrifice another whisp of hair!
It is worth this faff in the long run, trust me - get your shade right and you can have the hair you want for £5 a month for the rest of your life! Get it wrong and you have various hassles and expense getting it right before you can carry on. It would almost be worth buying 2 more shades and doing 2 different strand tests to really be spoilt for choice. You are in an enviable position of having all-natural hair - its much harder to change colours and mess about when you have some of it dyed because it reacts differently to the natural hair at the root, and you get root glow, and all sorts of problems so take the time to get it right now.
Try not to focus too much on the models on the box - bet they haven't used the dye on previously natural hair anyway - you want to focus on how light, and what tone. So what you have is the right tone but not light enough. So you want that natural tone (not too ash, not too gold, somewhere in the middle) but lighter than a medium blonde