That is ridiculous. I am BMI 21.96 (but my conversions of metres (1.75m) to feet and inches and kg (65kg) to stones may have been dodgy) - which is middle of "ideal". But whenever I go clothes shopping, I am always beyond a "Large" size. If they only have Small, Medium, Large - often I don't fit the Large...talk about depressing.
I am on a "diet" - just trying to be good and exercise every day - because I am bigger than I would like to be.
Just go with how you feel about yourself, I say. Bugger the scales and the BMI.