What's more reliable, a mirror or a scale?

I've been training a lot lately now my BMI is 19 and have a body fat percentage of only 18%. But when I look in the mirror I still see a bigger girl not that I have excessive fat hanging but I just look big. So should I follow the mirror and keep on losing weight? Or just maintain my weight and keep a healthy BMI?
What's more reliable, a mirror or a scale?
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