How can I list on my CV that I graduated from college in 3 years?
There are no magic words - you just say that thing you want to say.  The simplest way would be simply to specify the years you attended university, and then explicitly note the achievement you want to highlight.  One thing to note is that there is little point in mentioning this unless you have some statistical evidence that graduating within three years is actually a genuine achievement.  Try something like this:


  Education
  
  Bachelor of Doing Things (Oxbridge University) (2016-2018) Graduated with a GPA of 3.61 and won an award for being the top student in my third-course on doing good things.  I was in the cohort of 3% of student who successfully complete this degree program within three years.