Hi, and welcome to the Sportbike Forum.
To quickly answer your questions:
1. Should you be worried? No. You've taken the first step to becoming a responsible rider (we hope at least) by taking a course with PRS. Many of us on the forum were former students and still ride to this very day.
2. Don't sweat that bike you picked up. The R6 is an excellent bike. When you take your course, you'll start out on a 250cc bike but make sure you tell your instructors what kind of bike you have. If they are confident in your riding abilities, they will put you up on a bigger bike.
3. The helmet - Make sure it fits
you properly. Not all manufacturers are sized the same nor are their fitment designs. This will be talked about in your class at PRS.
Although this was brief, there will be more members with more experience and wisdom who will chime in. Congrats and welcome again!