I know I wrote a lot but if you don't like it... just simply don't answer?

I think it sounds like you felt more shy and less at ease around this girl than around her friends and yes, I think it is possible she felt a bit rejected by this. This is not anyone's fault. I felt very much like this with someone when I was a teenager and I really wanted to reach out to her but the more I thought about it the harder it became to behave naturally around her and the more the gap grew. From her perspective she may feel you feel negative about her and she has become more distant. I do not think you should make a big deal about this but see if you can work into a conversation with a group of you that sometimes you get shy for no reason and it bugs you. Or say to a mutual friend that you really like this girl but you get a bit shy round her and you think it has caused a problem - this may cause her to warm a bit to you as you would be making it clear your reticence is about you and not her?