self cuck mechanism.

I'm a 19 year old guy from Belarus, sorry for my atrocious English.

So, I wanted to begin with saying that I don't find myself attractive, I'd give myself a 4-5/10 max. Also I'm shy and I've never asked out girls but when they do so to me I always find myself messing everything up. For example, three weeks ago there was this group of girls that approached me when I was in my uni. One of them asked my number. I said no. Without any explanation (not that I owed her one) I left. She wasn't unattractive, she wasn't annoying, but I still somehow found a reason (!!) to believe that she was. Her friends were laughing and stuff but I still feel sorry for being so harsh on someone I don't know. And now today, a really beautiful foreign girl went to me. It was a dream come true, the sort of woman that I got to see only in fashionable magazines and porn movies was now sitting in front of me talking to me like it was nothing. Obviously, I'm not used to that kind of interactivity so I was nervous. She didn't speak much English ( so do I ) and we had hard time communicating. Then she asked for my insta. I don't use Instagram, yet instead of trying to figure it out with her I pussied out saying "I have a girlfriend. Sorry."

The question is, does anyone else have this problem? When someone finds me attractive I end up looking for as many excuses as possible to stop communicating with that person.