This is completely ridiculous. Don't send him back to the tutor. If he's doing the 11+ in a couple of weeks the most important thing for your son is confidence.
If I were you I would give him a few things to do at home to keep him ticking over and make sure he understands all his maths terminology (mode, mean, median, range, properties of different types of triangle, shape names, how to calculate area, volume etc). If you want him to do Nfer paper A, then get him to do it at home. Mark it (without telling him his score) then give him a list of questions he's got wrong and ask him to have another look at them. Then you can focus on explaining the ones that he genuinely doesn't understand rather than the ones where he hasn't read the question properly or has made a silly mistake.
It's impossible to tell if a child's practice scores reflect their actual ability or if they are so bored with the whole thing that they aren't putting any effort in. That aside, 82% is a very respectable score in a maths Nfer paper. My DS, who is also doing the Kent test in a couple of weeks, usually gets around 84% and it didn't occur to me that there was a problem with that. I've kept his older brother's scores on the Maths Nfer practice papers - 72%, 65%, 84% and 64%. His comment after each one was, "but it's only practice mum, I'll try harder in the real thing". He got a very high score in his real maths 11+ paper.
My 10 year old was going to a tutorial centre weekly, during term time until the end of June. He hasn't been since and we've probably managed to do the equivalent of 4 or 5 full test papers since then. I feel a bit bad that we didn't manage more but there's no point in worrying about it now. But two hours a day is just completely barmy!!
The 11+ isn't like cramming the day before a school test where you can memorise all sorts of facts and figures for regurgitation the following day. I firmly believe that, this close to the exam, there isn't much you can do and there's no point in worrying over what you could or should have done in the previous months. Focus on the things you can do something about - building confidence, keeping them relaxed and, as I said above, making sure that your child understands maths terminology.
Soon be over!