If you were fasting for only one hour when you first went in, chances are they did not get an accurate read. Generally, you should fast for 8 hours before testing - which is why they usually do AM appointments so you're only missing breakfast.
165 is elevated. 200 is definately not the diagnosis statuate for diabetes. 120 or 125 is probably closer to a normal blood sugar for someone who is not diabetic, fasting. If you had eaten only an hour or two, or even a few hours prior to testing, chances are you may be in the clear. Your body's natural insulin does not immediately take control of your blood sugar levels.
Your pancrease creates insulin when it needs to break down the sugars. The process does not spread throughout your bloodstream that quickly.
If you can't handle 3 hours, ask your midwife if you can snack on something like raw carrots (very low in sugar and carbohydrates). What raises your blood sugar is food that contains sugar; however they also may want you fasting so that they can receive a more accurate read. They may not be able to read certain tests if there is food in your system. They don't want you to walk around because exercise will cause your blood glucose to lower, and they do not want additional factors affecting the quality of test.
It would not be wise to skip the test. If you have gestational diabetes, chances are you will have to take insulin. It will not be easily controlled by diet alone. If your blood sugar levels are not contained within a normal level, it will put your baby at risk. There is a birth defect called holoprocencepholy (sp?) that is common in babies born to mother's with Type 1 or gestational diabetes whose blood sugar levels were not in proper control. This birth defect often creates cleft lip, breathing difficulties, abnormalities in the face, many health problems, and can cause your baby to be stillborn.
The only way that your "not so healthy" diet could have effected the blood glucose level is if you do not have enough insulin producing (which is the result of diabetes).
3 hours will be a small price to pay to ensure that your baby, and you, are healthy. For your sake, and your baby's, I hope the results are negative. If they are positive, be thankful that it is gestational diabetes, and it will not continue throughout your life. It will also help your doctor's keep a closer eye on the baby and ensures that you are both in healty condition. You get your own birthroom, which is like heaven these days.
Please go to the test. It will be better in the long run. I hope all goes well. =)