Hi Cindy,
I just started the workout yesterday also and it took me over a half hour. However if you look at the book, it breaks the exercises down so your doing something like 4 exercises a day, with 10 reps. I don't think you have to do all the exercises in one day. i could be wrong but that's definately over 15 minutes!!! I think you probably pulled a muscle in your chest. I know I'm definately breathing extremely deep, so it definately is possible. I wouldn't worry. I once pulled a muscle in my chest and I would get sharp pains. It went away after a week or so.