I don't know this spell, so I can't say for certain, but just because a spell is ranked high doesn't mean it works. A person can rank their own spells, make new accounts to rank their spells high, or ask their friends to rank their spells high. Doesn't mean it works.
Some weight spells do work, but more of an extra push. All weight spells work provided you change your diet and exercise regularly. I posted a weight loss aid on here [note I called it an aid not a spell] I've done it many times, it works for one month and helps cut down on cravings. This doesn't mean anything though if you don't put forth effort and fix what needs to be. Cast the spell 100 times, believe with all your might. Without you doing something it won't work. All working spells to have softer hair, cleaner skin, or a slimmer build, typically speed results. If you cast then sit on the couch of course it won't work.
Try the spell again, but go in with a plan. Make a work-out routine and a meal plan and stick to it. Don't starve yourself [its better to eat 5 smaller meals] and don't over exert yourself either.