I am not a doctor but as far as I know, saying 6.2 is prediabetic is jumping the gun a little. 6.2 is not particularly high and getting a single fasting reading is like taking your blood pressure once. Some days it's higher and some days it's lower so maybe it was just a bad day. A glucose tolerance test is a much more accurate indicator.
EDIT: Sorry the above assumes it was a fasting BG, not HbA1c. I suppose it probably was HbA1c which does mean you're prediabetic.
Even if you are prediabetic, don't panic. There is a huge difference you can make, especially if you start early, as to how fast it progresses or even in some cases reverses.