Sorry, I don't know all the Mac equivalents, but there must be some way to get the right-click context menu.
Until you find out how to get the context menu on the Mac, you can always select a row and use the menu: Insert > Rows.
To find out for sure where the "end" of your data is, type Ctrl+End (I think the Mac equivalent for Ctrl is "Cmd"). That will take you to the cell at the bottom right corner of all the data in the sheet. My guess is that it won't be on row 383. If it is on row 383, then I'm out of ideas.
AOO 4 • Linux • Fedora 17