I've just been diagnosed too (I'm 15 weeks pg and had the test early as had GD with my son a decade ago!).
It doesn't automatically mean you'll have a section - my first child (where I prob had GD but was v borderline under when I had the GTT) was ten days late and a waterbirth and my second child (where GD was diagnosed, as I said) was four days late and a v speedy natural (hospital) birth. Both weighed 8lb-something.
I hope that gives you hope that you may v well not end up needing a section!