Motion sickness was a concern for my wife on our first cruise. In fact, it was the chief deterrent for us waiting so long to take our first cruise. She went to her DR. and he prescribed some "patches" that worked very well. After two 7 day cruises, we had the opportunity to take a 3 day cruise to nowhere on the Holiday, the smallest of Carnivals' fleet. Due to the short notice of the cruise, she had no time to get a new prescription for the patches and went without any seasickness medication. It was then that she found out she really didn't need any meds. No problems at all. Now, she take nothing for the motion when we cruise.
Point being. She was afraid she would get seasick, but really didn't know. It's always best to be prepared though. The cabin stewards and the medical department have the over the counter varietiy of meds available, but we've never had the need. Go prepared, but not scared. The first cruise is the "ice breaker," and chances are, we'll see you on this board, in the future, giving good advice as a seasoned cruiser.
Go, and have a ball, (and don't worry), and let us know how it went.