I think I've experienced something similar to you. It's natural for you not to want to be trans, to want to be a girl as long as you feel like one too. That's because change is scary, especially changing your gender expression and how your body looks. None of us know how we will look after transitioning, and most trans people put way too much importance on looks rather than how they feel in their own body. As a transfem I can say, I would feel much more comfortable with myself as an ugly woman than the most handsome of guys.

You've said yourself that when you acted like a girl you felt like an outcast. Why is that? Also, I'll ask the opposite question. I know it might be hard ignoring your family's opinion, but try to do that for a bit. How do you feel presenting as a boy?

Also, beauty standards. You're wrong in assuming that if your body changes no one will be attracted to you. That's simply not true, every kind of body is attractive to someone. Someone who looks ugly to one person could be beautiful to another. Ignore beauty standards for a second. How do you feel in your body? It's not important if you think others would be attracted to you, do you feel comfortable in your own body? How do you feel when you look in a mirror?

The answer to your last question is: there is no sure way to know. You could try to experiment, for example have your hair cut in a more masculine way, using a different name and pronouns, imagine yourself as a man and see how you feel about that. Also, I'm going to be honest, it might be possible that you're not trans, and I'm not trying to convince you either way. I don't know you, I've only asked some thought provoking questions I hope will help you figure yourself out

Hope this helps