Hey Devon,
I've also experienced the social isolation and anxiety you talk about, as well as the predominantly male peer group. When I was going through puberty I actually developed a severe phobia of women around the same time I began experiencing feelings of being trans. In fact I'm almost certain they're related, and although I got over it a few years later I can still remember the fear I had of associating with women. As a result, my social circle was pretty much entirely made up of straight men for a long time. I think it's because I was in full denial of being trans, and was worried that any association with a girl in the form of friendship rather than sexual attraction would make people raise questions about me.
I have a very good female friend who I talk to all the time, and the relationship dynamic is definitely different to that of my male friends, especially when it comes to discussing personal matters. Like you, I find that there's a very different dynamic in my relationship with my female cousins and friends than with men. That being said, there's nothing wrong with having a male peer group and while many trans women gravitate towards female friends from a young age, it's hardly a requirement for being transgender. You absolutely deserve to be who you are, and I know that the nagging doubt that's there when it comes to making big decisions can make it seem like it's impossible.
As for attracting more friends, it can be very difficult and challenging even for those who aren't going through what we are. If you're anything like me when it comes to social interaction, as in you're introverted and shy away when possible, it can be daunting. I've coped with severe social anxiety for most of my life, and even after several bouts of cognitive behavioural therapy I still have trouble. However I've found that the best way to deal with it is to simply push yourself to talk to new people. I'm sure you have acquaintances in your life that could become good friends; try and talk to them, ask them about themselves and show an interest in what they like. You'd be surprised how easy it can be to go from simply knowing someone's name to being introduced to their social circle and begin making new friends.
If you ever want to talk, feel free to send me a PM when you hit 15 posts, I'd be more than happy to chat!