Hi I haven't done this particular tour although I have been to Cambodia and Vietnam with JY and absolutely loved it! What's more, the tour manager I had in February told me that the tour you've chosen is his very favourite and he has been working with JY and Travelsphere for 23 years so he should know what he's talking about!
There's no need to be nervous, you have made a great choice for your first JY tour. Once you arrive at the airport and meet some of your fellow travellers, all your nerves will disappear and you will, I'm sure, have a fantastic time.
All the best,
Bob