When things go wrong.

Last night Bear pulled me across his knee in bed and started his usual bongo session to some sort of tune on my backside.  After he had warmed me up he reached for his belt.  Maybe after six strokes he miscalculated striking my thighs instead.  The spanking wasn't very hard and we were both having fun.  Until Bear noticed my legs were bleeding where he hit my thighs.  He felt terrible about it and I reassured him it was no big deal.  At that stage it wasn't hurting or anything. I had trouble falling asleep as the pain intensified during the night and there was actually blood on the sheets.  Bear was horrified he had caused this and even today feels shocking for doing it to me.

Has this happened to anyone else?  How can I make Bear feel better about this situation, as I don't want him turning against this lifestyle for fear of hurting me in the future.