Pretty hard to say how empty a flight is from the Expertflyer load, as seats available for sale is never shown as higher than 9, so 9 could mean 9 or 19 or 90.

F4 A4 J7 C7 I7 O0 P0 Y9 E9 R9 W9 M9 B9 U9 K9 H0 Q9 L9 T0 V0 X0

That being said this flight looks semi-full given no T, V or X availability, though as it is last minute that may also be the reason. Looking at the seat map there are several center rows which are completely open, probably about 40-50 open seats in total, see seat map below. What I'd recommend is to change your seat assignment now to an aisle in one of those rows, trick will be to prevent someone self-switching to the opposite aisle, to be fair the kind thing to do is to just go for 2 seats, there's probably enough open seats that pretty much everyone can get 2 (or 1.5 in the sets of 3 along the windows, open middle):