Something suggested in the book of The Secret, is to create a sticker or similar with your ideal weight on it, and cover up the dial result with this sticker, so that every time you get on the scales to weigh yourself, you are your ideal weight. You could also perhaps record yourself saying "I am my ideal weight of x and I always eat and exercise properly to maintain this" and let it play in the background while you are at home (assuming you are able to do that, otherwise listen to it on an mp3 player over headphones). It may be that there is an underlying hidden belief within you that does not actually believe in the target weight you have identified for yourself, in which case, both of these suggestions will help to create a new reality for your mind that then manifests in your life.
Hope that this helps and you achieve your goal.
Best wishes to all
Cheryl-Anne