I really wouldn't say that, at least not in that way. It will generally be heard as "Please provide more reassurance that it won't inconvenience you". If I've offered something and am thinking better of it, there's still no way to respond to "are you sure that's OK" with anything other than "yes, I'm sure that's OK", and I resent it all the more for being forced to say that. Alicorn's suggestion is good.