The problem of being Mafsik where Moshe Rabbeinu wasn’t, is by Krias Hatorah. Otherwise, as ItcheSrulik pointed out, you’ll barely find a whole Passuk quoted in Sefarim.
ItcheSrulik, the Issur is to sing it, not to write it. The Peshuto Shel Mikra of Shir Hashirim is not a reference to your wife, it is only meant to be understood as the relationship between Hashem and Knesses Yisroel. Singing it for your own purpose is the Issur.
I think you are implying that singing Chasdei Hashem Ki Lo Samnu with a bad tune or a bad place would be the problem. Why do you think it mentions Shir Hashirim if not for the fact that there is a reason people use it for a song?