Most of the empty seats you see are "preferred" seats that non-status pax cannot select in advance. All or most will likely be assigned close to departure, either automatically or by an agent. You can always hope your middle-seat mate will have requested an upgrade and get cleared just before they shut the door.

I would keep the seat you have, but check with an agent at the airport if some desirable seats are still open at that time.

A phone agent may also be able to tell you how many seats are sold but not yet assigned.