Hi juliav,
Its normal to be nervous before going for the first time however i assure you you have nothing to worry about. I have been on the Croatian Istrian Coast trip and you are in for a smashing time. The tour manager, Vlatka, is a diamond and the county is amazing.
When you arrive at the airport you will quickly find other JY'ers who are in a similar position and your worries will melt away.
If you have any questions let me know.
Mark