So I accidentally grabbed my 40 volume developer (needed the 10 volume developer) to color my hair a shade or two darker. The color is Ion Color Brilliance - Permanent Hair Color 3G-3.3 Level 3 Dark Brown gold tone. I immediately washed it out. By the time I realized I used the wrong developer, I had already done the top half of my head. At the moment, I have a little scalp irritation (to be expected). It doesn't seem to be lightening at all...

What would happen using a 40 volume developer when coloring hair darker? Would it lighten or just stay the same? Any advise of what I should do now to achieve my darker hair color? (no box dye users, plz)