IIRC the Kamasutra says there's 3 genital sizes for both men and women; big (horse/elephant), medium (bull/mare) and small (hare/deer). It says you can have great sex with up to 1 size difference, and although the woman being one size smaller is preferable to her being one size bigger, it calls equal unions the most perfect ones. And that's just refering to vaginal intercourse itself, of course there is so much more to sex.
I don't know what my point is, other than: don't fret! If you find someone you like, and who likes you, a lot of silliness and unfounded fear will fade away.