If your legs are longer than average, the cockpit may be too small for you. The 8.5 would probably solve this for you, but it's a slug of a boat. It's not a bad boat, it's just not a very responsive design.
You said that your foot board is almost all the way forward. Try moving the board all the way up and get back in the boat while wearing your river shoes. It's ok for the fit to be a little snug. You'll want your thighs to brace up snugly into the thigh braces. It will feel awkward at first.
Have you been out on the river with your boat yet? If not, I would recommend signing up with a club or a commercial operation that specializes in teaching beginner kayaking skills before you go and buy another boat. Or, go with a friend who is willing to instruct you. This is an essential part of learning to kayak. These folks can help you get fitted to your boat while you are learning. A commercial operation might even have other boats for you to try out as part of their package of instruction.
Welcome to the wild and crazy world of whitewater kayaking!
Do unto those downstream as you would have those upstream do unto you.