To quickly assure yourself of the current logical resolution: Press command-shift-4
CMD+Shift+4 to capture part of the screen, and the coordinates will be shown next to the cursor. Move the cursor to the lower right corner to the see the resolution (you will have to add one to each coordinate).
Alternatively, in this same mode, drag from one corner to the opposite one to select the whole screen, and the size will display in full, no addition required.