I think it's great that you have a fiancé who loves you at such a young age, especially considering that a lot of people with Asperger's Syndrome find relationships hard. Don't rush anything but I would advise you to try kissing her, and then at least if you don't like it or still think it's gross you can decide what to do about it with your fiancé.
Kissing is easy though; there's no need to be nervous at all. I know it's easier said than done, 'cause I was worrying like mad about my first kiss (and I don't have AS, so I can only imagine what it must be like for you) but honestly, just do it, and she will be so excited by the fact that you're kissing her, she won't be marking your technique! Kissing comes naturally. I hope your relationship with your fiancé goes well, my friend.