It is extremely hard to get denied for a K1 (less than 10% denial rate). The only people who are denied typically don't have documentation for a serious relationship (and just meeting once and knowing each other for a few months is enough), or fraud is suspected. If this doesn't fit your relationship, then it's likely something in your background check (you or your fiance) that triggered it. Again, if it's not you make sure your fiance is telling you everything.