I'm sorry you're dealing with so much uncertainty :( Please try not to feel like you did something to cause a high number (one high number, that is all you are looking at right now - you could potentially retake that test today and get a totally different result)...I have known lots of people diagnosed who ate well and were healthy weight, and lots of people (me included) who don't eat as well as they could and/or were overweight, but passed with flying colours (although, on a different day or with a different breakfast, maybe I could have failed the screening too...it is just a screening, and very unreliable). Did you do the screening fasting? Some care providers instruct you to fast, others to eat normally, others to eat a light breakfast....what you ate most recently and how long ago that was could impact your result on the screening as well.
Also, it varies by practitioner, I guess, but I've never known anyone with GD who's been automatically routed to a c-section. Induction a bit early is more common, which of course carries its own risks. Especially under midwifery care (is your midwife working under ob/gyns? or independent? that would make a difference, I imagine), a GD diagnosis doesn't seem to risk you out of everything other than c-section. I am pretty sure I'm not going to take the test at all, and I asked my midwife what that would mean for my care given that I have big babies (despite passing all the GD screenings!) and am plus sized...she said it won't affect me one iota (nor would the diagnosis, assuming I kept my sugars in check).
Something I find helpful to remember is that I have to consent to these types of interventions. No matter what happens, if you are truly not OK with automatically going to a c-section or being induced at 37 weeks, you do have the right to refuse that and come up with an alternate plan that you can feel comfortable with. If your care provider says it's 100% their way or the highway, it's a clear sign that you might want to shop around for someone else, cause even if you pass the 3 hour screen and avoid a GD diagnosis, an attitude like that can be a strong predictor for more conflict as the birth draws nearer. JMHO. I hope that you will get great relief from talking to your midwife next week, and this paragraph will therefore be moot ;)