Can I get botulism by using 2 cups vinegar to 8 cups water when canning pickles - as most recipes require 1:1 ratio of vinegar to water?
While no one will tell you if you will get botulism or not, it's the acidity in pickles that makes them safe.  According to Douglas Baldwin
"Food pathogens can't grow below a pH of 4.0.  5% vinegar is 25% more acidic than this."  He goes on to talk about the pasteurization step.  You'll have to scroll a bit to read the section.  We don't know your vinegar's starting acidity, and you diluted it significantly....So, you would have to calculate the total acidity of your brine, beginning with the acidity of your vinegar, to determine if you are within the correct safety parameters.