Okay, so I’ve decided I want to tell her that I like her, but how do I go about it?

For starters, I’m in high school and nearing my senior year. I want to actually try and have a relationship for the first time. There’s this girl that I’ve liked ever since I attended the school and I actually want to ask her out. I’ve even caught her glancing at me (or if not the area around me lol) like three or four times already which is kind of what sparked something in my brain. Although sometimes I feel like I just happened to be in her line of sight while she’s daydreaming or something. Idk

Problem is, for the majority of my years in high school, I was the “loner” type. I sat alone at lunch and I did and still do have friends but its an on and off thing with them. I think most girls perceive me there as “reserved” and “unapproachable” probably and I feel like that’s a problem. I’ve changed a lot as a person though over this entire year.

How do I, a guy who’s been quiet and not as sociable as my fellow peers, ask out a girl I’ve been attracted to since freshman year?