Don't let anyone tell you you're 'ugly'.
Seriously, it's quite amazing how far your appearance can change in reflection to what your mind is like. Most genuinely attractive people I've met could just have easily have been quite easy to ignore if they hadn't carried themselves the way they did, and that's almost entirely mental or personality-related in nature. Equally, a lot of people don't seem that attractive until you hear them talk about something or notice a certain way that they think or an aspect of their body language.
For instance, it's virtually impossible for someone to look 'attractive' if they have their shoulders slumped and they're hunched over with their face pointed at the ground.
You can't really fake any of that though - if deep down you think yourself to be ugly, then to some degree it'll come out in the way you carry yourself. Believe me, I know it's hard at 16 (I still struggle to do it) but if you just try and accept yourself as much as you can, and once you're used to it it'll show - you can visibly tell the difference between people who do and don't. But my advice is, don't ever let anyone else tell you what 'rank' you are.