Joshua..
None of us will be able to diagnose you over the forum.. 6.4 mmol/l as a single fasting reading is a little high but that could be due to a multitude of reasons and not necessarily diabetes. If you are concerned then you best bet is to go to your GP and let them know you had a fasting test at the chemist and you thought it best to follow up.. They will then probably take some blood for an HbA1c test (an average of your blood glucose over the last 3 months) and also do another fasting or glucose tolerance test.