As a retired physician who specialized in sports injuries, I have treated people like yourself many, many times. I would say that the shore is your greatest concern. Most injuries, in fact, do occur on shore. Think about it....the round slippery river rocks. Before and during college I was a commercial river guide. We would have customers get bumps and bruises on the water but ankle sprains and more severe stuff on shore. If there is pain with lateral pressure on your ankle while in your kayak during maneuvers, you have to figure out how to pad yourself, maybe with a sock....or other like ethafoam within the boat. Maybe, consider a walking stick while on shore. Grab deadwood during scouts. Include a STOUT ankle brace as part of your "gear". You should have no problem.....go out and learn that roll!