I can't really say that you can trust results of box dyes, unless you've used them before. Even then, depending on many factors, it may still not turn out how you want it to be.
Starting from the beginning, if the colour you were after was lighter than you started out with, then: 1) use a colour remover if you have any residual colouring from past dyes, then 2) bleach or bleach-bathe with caution to get it to the lightness you wanted. Once it was a more even colour
value all over, perhaps a little lighter than you desire, then a gentle semi would have been the best choice to get the actual colour hue you wanted to achieve.
But it is all easier said than done!
At this point, I'd agree with the above advice, to use semis to achieve the copper you are after; I don't do copper myself, but I'm sure others can recommend a direct dye that would help get closer to the colour you want. Then, if the result is something you can live with, give your hair a rest for a few weeks (or more!), then remove all the colour and see if you can start again.
That's just my opinion, but I also have heard that 20-volume peroxide is high enough, especially if you're not after a light bleach blonde. Anything above that can be very damaging, and damage unfortunately does not show up immediately, so if your hair seems happy now, please still be gentle with it.
I also agree, it looks quite cool the way it is now, even at "50% better"!