@JohnM, this is a common feature which I've seen before unfortunately - because thre's no 2E on the 737, and possibly 2F was taken - perhaps from someone who was originally somewhere in row 1 or 2 on the 330 - then you got pushed back. And since you fell to LTG (as you identified) row 3 was probably all that was left (and possibly even if you were still WP when it happened, reallocating the seats assigned in J to the 737 probably filled up rows 1 and 2 as is, so you got 3. I'd assume 3DF are also filled, so you now have no real option to change.
it's a bummer for that sector of course to lose the 330, but at least you can just swap seats on board and both get what you want which is easy enough to do. I suppose you could look to see if there's a more appealing flight and see about changing (depending on availability and/or fees of course).