My BF and I did something similar, kind of. I actually met the parents when I met him a year and half earlier at a Scotland football match. BF and I have a common friend which is how we met. Anyway, when we started dating, things happened really fast and within a few days I found myself sitting down to a proper dinner with his parents. The strangest part of it all, was that it didn't feel weird. It wasn't until days later, when I was traveling on a train alone, that I reflected that by American standards, or at least my American friends' standards, meeting the parents that fast is a bit odd. Oh well, they are lovely people and it seems to be all working out.
I hope you have a wonderful time and I'll keep my fingers crossed that the weather is nice (since I'll be over the pond at the same time) *wink, wink*