See if someone can help you. I got a big splotch on the back of my head because I couldn't see what I was doing.
If you use a cap, don't pull too much hair through! My aunt did that when she was helping me and I ended up blonde with brown highlights.
We also waited twice as long because I thought I should be able to see the color before I rinsed it out. Did I mention I was platinum blonde when my natural hair color is about 2 shades lighter than black?