Nope, it's not your height. 6 feet is definitely tall for a girl, but it's not freakish deformity tall. People will definitely notice it, but your height alone isn't going to scare anyone away. It's something else entirely.
That something else, and you said it yourself, is your total insecurity. I know you said you're only a little bit insecure, but you also said you're a girl and that's what completed the statement. Because if a girl says she's a little bit anything, it means she is totally that thing. When a girl says she might be a little bit bittchy, it means Judge Judy is nicer than her. When a girl says she's a little bit picky, it means most gorgeous billionaire movie star guys wouldn't meet her standards. And when a girl says she's maybe just slightly insecure, well... you get the idea. You know I'm right.
That's the thing you need to get over, because that's the reason guys aren't asking you out. If you ask any successful celebrity, rock star, pro athlete, businessperson or whatever what their secret of success is, they'll tell you it's 90% confidence. Confidence is honestly the most attractive feature anyone can have (as long as they don't have too much), because people are naturally drawn to confidence.
I used to totally lack confidence and now I have plenty, so I know. There was a long period in my life where I wouldn't even look the ugly girls in the eye, because I had no confidence in myself. I finally got sick of being ignored (even when there were only two other people in the room), so I broke out of my shell and never looked back. Now I'm a locally famous (well almost famous) rock star, a celebrity at work, and definitely the best lover never mind how many girls have ever had. All it takes is a little bit of self confidence. If I could do it, and I did, so can you.