I am pretty self conscious about my looks, but there's this very attractive girl who clearly finds me good looking, so does this mean i'm at least average?
No just because she is attractive and likes you it doesn't mean you are. You may be thinking you must be in her league but you can't plan who you are attracted to. Forget worrying about how other people perceive you and be content with the fact she likes you.
I am pretty self conscious about my looks, but there's this very attractive girl who clearly finds me good looking, so does this mean i'm at least average?
No. It means one human being out of billions finds you attractive. So like 1/7,403,738,157
Does OP feel that said girl is thinking in advance and that choosing guys near the level of attractiveness as she is will create beautiful offspring? Who could blame her.