If possible, I'd recommend spending some time just diving a simple, safe location to get comfortable. Whenever I need to try something new with diving, be it equipment or a new technique or something, I go to a lake, where the water is still and not very deep, and I spend an AL80 or so familiarizing myself with whatever it is. Obviously, bring a buddy for safety, but ideally your buddy would be a friend or someone like that, that way you're not stressing about inconveniencing a group or a dive guide.
Calm will come in time, and once you're comfortable with the still, shallow water, start heading deeper, or to places where there's faster currents.