Hello
I totally understand you. I was in the exact same boat. in fact I had my 3 hr on Friday and Saturday baby shower too. I only got the results from my 3 hour one the following Tuesday so that left me enjoying the baby shower on Saturday with cake and all the good stuff.
Here is what happened to me . At 1 hr I had 136 I should have had 130 according to new limits. In the past used to be 140.
For the 3 hour one I did not prepare in any special way except fastening after 12 pm like they told me.
What I did different than from the 1 hr one I drank water. Both nurse and doctors told me I am allowed. so after I drank the nasty drink I drank water then they drew blood every hour. I think the water helped a lot and if you really have GD you cannot cheat, the numbers come high and you might get sugar in your urine later on too.
so if you barely failed good news is you will mostly likely pass the 3 hour one. Good luck and enjoy your baby shower