I really need help coming out to my parents!

Okay, this is my first time posting in a forum, but this has been bothering me for a while.
So, I've just recently realized that I was transgender. I've felt uncomfortable being a girl for a while, probably since middle school, and it got worse when I started high school, but it wasn't until a few months into my sophomore year that I actually came to terms with the fact that I'm trans. I was researching transgenderism and FTM transitioning like crazy, and I knew that I definitely want to transition at some point. The first person I told was my girlfriend that I've been going out with for about seven and a half months now. She was really supportive, and she told me that, even though she sees herself as a lesbian, she loves me as a person, not because of my gender, so she'll help me through everything. After her, I told three of my friends, and they were generally supportive, as well.
I really want to tell my parents soon, but I don't know how to tell them, and how they'll react. I realize that it's kind of soon, seeing how it's been a little less than a year since I figured out that I'm trans, but I am sure about it.
I know that my mom is accepting when it comes to transgender people, but she doesn't know any personally, and I don't know how she will react because it's me. I'm her only daughter, and she went through another risky pregnancy to have me (she had HELPP syndrome when she was having my oldest brother, and my other brother wasn't very healthy after his birth; the only reason she wanted to get pregnant again was so that she could have a girl). I think that when she finds out that I'm trans, she's either going to be depressed because she'll feel like she's lost her daughter, or she'll refuse to believe it. I told her that I like girls a while ago and she seemed fairly accepting, but whenever she brings it up, she says that I "claim" to like girls, not that I actually like girls. And once, I walked up to her wearing a fake moustache and said "I am your third son!" She looked really upset, and said "No! I got pregnant again to have a girl!"
But, at the same time, she's confusing me because she might actually suspect that I'm transgender. I told her that I watched a documentary on transitioning, not telling her the reason why, and we actually had a decent conversation about it. Then, a few weeks later, there was an article in the newspaper about transgender kids. She handed it to me to read, which wouldn't have been that weird because she knows that I was interested in transgenderism, but she also gave me a weird look when she gave it to me, like she was waiting to see my reaction or something.
I'm also worried about telling my dad. He keeps calling me his "little girl" all the time. I like that he's being affectionate because I don't see him as much as I see my mom, but I cringe whenever he calls me girly things.
I see a therapist, mostly for my anxiety, but I told her that I'm transgender. I was hoping that she could give me advice for telling my parents but, unfortunately, she didn't even know what being transgender meant. When I explained, she asked me to explain why I'm transgender. It felt like she was asking me to prove what I told her, which I can't. I don't think she'll be a lot of help when it comes to this.
I'm going in my junior year of high school, and this is the year where I should start looking into colleges that I'm interested in. I was searching for colleges that are transgender-friendly, that would help if I decide to transition physically in college. If I told my parents that I want to apply to those colleges, though, since they're not the ones that would necessarily be the first choice for what I want to go into, they might wonder why the colleges are important to me or why I tell them that I really like them. Plus, there's been a lot of gender dysphoria, and it kind of makes me depressed that everyone treats me like a delicate girl and that guys feel weird when I hang out with them.
I feel like telling my parents would be a huge step, and I just really need help with all of this. My girlfriend told me that I should tell them when I feel comfortable telling them, but I don't think I'll ever quite feel comfortable telling them because I'll be afraid of what they'll think.
I'm sorry that this is really long, but if anyone has any advice for me, please help! :help:
-Adrian

 

Hey, thanks for your response! The problem with saying it like that, though, is that when I was younger, I was actually pretty feminine. I don't know if it was because of the way that I was expected to be extremely feminine at a young age or because I actually did feel feminine (I don't really remember much from when I was really little), but my parents still think of me that way, as their little girly girl. My room was pink before I painted it, and I wore pink a lot in elementary school and before that. So, I can't really say that I've always felt masculine, because I haven't. I just know that I would feel more comofrtable in a male body, and that I am who I am. I'm not an extremely manly person, just like how there are guys that are more feminine. The fact that I'm not the manliest person, though, would probably make my parents think that I'm not really transgender.