Rule of thumb on manuscripts as I know it:
If the manuscript has not gotten out of the lab to a journal, the ms is "in preparation."
If the manuscript is under review by the editors and reviewers, the ms is "submitted" to that journal.
If the ms has been accepted for publication by the editors and reviewers, the ms is "in press."
If the ms has been posted electronically, make a note that it is both "in press" and an advance copy has been placed online. If the journal is an electronic open-source or doesn't print articles anymore, then it's published online.
And yes, absolutely make sure your PI mentions your contribution to the pending manuscript.