I recently got certified (October) and honestly I was not really concerend about any of the skills. For some silly reason I was more concerned about how I looked in the 7 mil black (form fitting/form smashing) wetsuit than I was about the diving. I guess I figured that there has to be somebody that mastered this skill who was worse off than me at some point.
Plus I knew that my dive instructor was going to make sure that I did not die so I was ok with that. Once I got to the dive site and in the suit, I realized that all of the other divers and class mates were not paying any attention to how I looked as they only wanted to talk about visability and water temp.
Once I got in the water I was rather giddy and ended up having a great time. The only thing that I struggled with was remembering not to hold my breath (it is underwater afterall).
Making the ZZZ (or AHH) sound took a few reminders from the instructor but I caught on.
Just remember that you did all of the skills in the pool and you can do it in the water. Wherever you are doing the checkout dives is really just one big pool and there will be so many people there keeping an eye on you that there is no need to be nervous or concerned.