Being honest here, I only skimmed replies, so apologies if any of this is repetitive.
Something about having your own first horse is, in itself, pretty intimidating. I took lessons on all kinds of different horses with their own habits. However, when I got my first mare (who was old as dirt and quick as a whip), I just didn't seem to have that confidence. She was very forward and, one day, did a few little bucks with me on the trail. Between my trainer's husband being an over-all ******* and the general intimidation I had, I ended up refusing to get on her for probably six months. It took a big chunk out of my confidence.
Don't lose hope. You will get passed this. Your first horse has a lesson to teach you and that lesson is confidence. Take a deep breath and take it easy. There's no reason to rush things. You do have to push yourself out of your comfort zone, though, even if all that is is having someone observe you walk her around an arena for 15 minutes. If you need to, take baby steps. There's no reason to feel like you should be able to gallop - or even trot - across an open field without fear. Don't give up on her and definitely do not give up on yourself. Pace yourself, relax yourself, and remember that your fear is just an emotion and with training, you'll be able to work yourself passed being stuck in that state of fear. (Don't get me wrong, there will always be moments that might scare you or give you the butterflies; it's normal and human.)
When you ride and you feel tense or nervous, take up singing. It doesn't matter if you're any good at it. What it does is give you an outlet for whatever is inside you while giving you something else to focus on. It's like a time-out without stopping what you're doing. Sometimes even just talking to your horse can do the trick. Overall, the point is relaxing yourself so your horse can stay relaxed as well. This will make things progress easier for you both.
I hope to see future posts where you can't shut up about how happy you are with this horse. Good luck and if you ever wanna talk, feel free to shoot me a message. :)