Nancy -
It sounds like you simply had a very inaccurate test and an tester who did not know that they were doing. Now with more information from you to go on, it seems like you do have things under control and 18% sounds much more reasonable given your weight.
To tell you the truth after I wrote my earlier response I was worried I sounded too harsh. A short post usually does not tell the whole story but I was worried you might follow that bad advice you were given and set yourself up for some serious health problems. At minimum I wanted you to get a second opinion about that 11.8% number.
I'm glad I was worried for no reason.
I almost forgot ---
I agree that body fat testing is the best way monitor your body composition without getting hung-up on the numbers on the scale, especially for women who carry more muscle than average.
I too carry more muscle than the average woman and usually weigh more than most women my height. For example, my mother and I have the same waist/hip measurements and are the same height (we can wear the same pair of jeans) but I weigh about 15 lbs more than her and have a lower body fat percentage.
Focusing on my body fat percentage helps relieve the anxiety when I see the higher numbers on the scale.
