I had blood work and my sugar tested 5.7, why is my dr. Saying that I'm pre-diabetic when under 7 is the goal?

Complications. Anyone with a hemoglobin A1c of 5.7-6.4 is considered pre-diabetic. At this level, there are many things you can do to reverse the course of the disease and prevent the development of diabetes. Once you are a diabetic, the A1c goal is < 7 because beyond 7%, your risk of complications from diabetes begin to go up, especially the risk of retinopathy (diabetes eye disease).
It is a range. 5.7 to 6.4 is "prediabetic range. <5.7 is normal. 6.5 and above = diabetic...If you have diabetes, the goal is to keep below 7. So, at 5.7, you are at slightly increase chance of developing diabetes, eventually...So, healthy lifestyle is important.