Welcome, Matthew~

I would think that your first approach would be to talk with her about how you are feeling. Let her be aware of how her "over" affectionate behavior is effecting you. She cannot read your mind, of course, and by expressing yourself properly to her of your concerns & feelings, then she may understand how her behavior is causing you these issues....which can, if left unattended, become more than what it is at present.

Granted, there is nothing wrong with showing affection for another, but there is behavior which can exceed the mere "expression". And for a lot of men, especially, that physical expression (receiving the touch/caress of the hand gesture) can be misconstrued as an invite to something more.

Maybe your fiance isn't aware that what is harmless behavior to her can mean a great deal more to those who are receptive.....(and are happy TO receive).

This is a delicate situation because if your fiance is accustom to being physically expressive and views nothing wrong with it, trying to convince her how it is effecting you may create conflict. Let's hope not.
If she is understanding of you and your feelings, then she will have no problem of "taming" her behavior...though, understand that adjustments of one's own behavior takes time to achieve...practice makes perfect.

When you approach her, refrain from using talk of "YOU are doing this or that", but rather say, "this is how I'M feeling", sorta thing. This tactic should prove beneficial .

Good luck. Wish you the best.

Shangrala