Whether in her dream or in the reality of being awakened from a dream, the woman has teasingly said to her shepherd lover at the door that she is not attired to come to the door. But something happens that stirs her; he seemingly opens the door. But…
4 My beloved thrust his hand into the opening,
and my inmost being yearned for him.
5 I arose to open to my beloved,
and my hands dripped with myrrh,
my fingers with liquid myrrh,

upon the handles of the bolt.
Because of 5:5, I don’t think 5:4 is erotic description; instead, the man has (as it were) knocked on the door, left her a token of love (myrrh), and she comes to the door and her hands find only the myrrh. Others suggest that she had anointed herself in anticipation of him — and that it was her hands that were coated with myrrh and then got on the handles of the bolt.
And because 5:6ff records her searching for him, I don’t think we can read 5:4 as anything other than the shepherd depositing a token of love at her door in order to remind her of his love — and her tardiness in responding to him.