How do i know if i have Diabetes?

I got tested in march and on the 6th of April went to a endocrinologist who said my blood sugar was at 164 and i was considered borderline diabetic what does this mean? also she said i could prevent type 2 diabetes with a healthy diet and exercise which i have been doing and have lost 8 pounds, i weighed 166 at the doctors office and now weigh 158. Also i washed my car and my mom noticed at night i had a dark ring on the back of my neck what does this mean could it just be from the sun? Please help me I'm worried :(. Oh and my moms side of the family has a diabetes gene which increases my risk, also I'm 15. And I have prickly feet and hands but this happens rarely like once a week. But according to the web its due to high sugar which i have. By diabetes gene i mean my moms side of the family has a history of diabetes all of them but my mom have it. Also when i went in the office they took a blood sample with a glucose meter and it read 128. And I ate at 11 p.m. that day a bag of baked hot Cheeto's and water bottle and i tested at 3-4 p.m