first of all, most weight calculators are the same, so as long as it was giving you a BMI value it should be right. There is usually a healthy weight range and some people are at different ends of the range. Also, these calculators are not totally correct because they can't look at your body frame size, or if you have thick or thin bones. Just because someone is smaller than you doesn't mean you are fat, you are just built differently. There are problems with being too thin just like there are problems with being too fat. I think that you are probably at a healthy weight, but if you aren't happy you can always jog, run or walk, and be sure to eat healthy (cut out most junk foods).