I don't think that's true at all. Beauty is in the eye of the beholder, and what some people may find unattractive might be seen as beautiful to another person. Like, I'm sure there are people out there who don't think I'm attractive, but there also are people who do. Anyways, true beauty comes from within and how you feel about yourself. :) Don't let anyone bring you down.
It depends on why they find you less attractive. If it's because you aren't as physically attractive as some other girls, then whether you have less quality or get less out of life will depend on how good you are at ignoring others' opinions and just doing what makes you feel proud of yourself.
On the other hand, if people find you unattractive because you have a nasty personality and are terrible to be around, then you will have less quality of life because you are encouraging the negative.
So if it's because you don't have a good ass then you can be happy and just need to find what makes you proud. If it's because you are an ass, then you may want to develop the better elements of yourself.
No, that is no true. Since attraction comes from inside and you can control it and if you love yourself the way you are, you will be attractive to other people too. I mean think off famous people who are not good looking or attractive but have achieved a lot in their life.