You are who you are, and that's what you need to accept. Yourself.
The feeling you get when you feel like you're ugly, stems from the dissonance between who you perceive yourself as an what you believe that the rest of society expects of you. And those expectations are so varied and high, and even contradicting, that you'll never reach them. No one can make everyone happy and there's no reason to even try.
That's why accepting yourself as who you are is the best thing that you can do. And that includes to accept that your are beautiful the way you are.
Of course there will be settings in which you have to adhere to the norms. I'm expected to wear a suit to work, preferably dark blue. I'm expected to shave or have a proper beard. I'm expected to act and behave in accordance with the values and the image of my employer. And that's fine. It's not really hard when you learn the rules.
You can treat the rest of the world the same way. Your grandmother has some expectations for you. And your family, your friends, even strangers. You can choose who you want to make an effort to please, and usually you'll naturally behave differently around your 80 year old grandmother and your friends. That's normal.
But remember that you are you. And you should stay true to yourself. That's not to say that you can't follow trends or norms, but don't do things you don't want to do.
Your beauty and value doesn't come from how others perceive you. It comes from your inate value as a human being. Embrace yourself as who you are, because you deserve it.