I failed the one-hour screening, as well. I had a 142, but my midwives have a cut-off of 140.
My midwives wanted me to take the test because I'm measuring ahead as well. I opted to take the 2-hour (they don't do the 3-hour test in Canada) because I'm in the process of moving from Florida to British Columbia (I'm currently in Santa Fe!) and I just didn't want to worry about checking my sugars and worrying about food if I didn't need to while we're driving across country . I mean, it's hard enough as it is, to be on the road for several weeks at a time, without having to be vigilant about every bite I eat, you know??
At any rate, the diagnostic test was a pain in the rear....well, a pain in the arm, actually, but I passed it just fine, and many many people who fail the screening test do just fine on the diagnostic test. My numbers for all blood draws were low-to-normal in all cases, with no numbers even close to the cut-off limits.
I cried and cried when I failed the screening test - I couldn't believe it! But the screening cut-offs are lower than they are for the diagnostic test, so you can fail the screening by quite a lot and still do fine on the longer test.
My midwives basically told me that whether I passed or failed the diagnostic test, I should take the experience as a reminder to eat well and make sure that I'm avoiding sugar and not eating too many carbs, and to make sure I'm getting regular exercise - even a 20 minute walk every day can make a big difference. They find that the majority of the time, their patients do just fine by making even subtle changes in their diets (i.e. eating sweets once a week instead of every day) and increasing their exercise levels. They said they only really worry if despite being strict about diet and exercise, blood sugar numbers can't come under control - but said that's pretty rare. It happens, and if it does, then it's something to take seriously, but don't get too far ahead of yourself!! In all likelihood, you will do fine on the diagnostic test, and you and the baby will be just fine with some tweaks to your diet.