The image should now be resized to your desired size. Your image might not be shown as 100% on the screen. Pressing Mac: command+1 Windows: ctrl+1 or will resize the your view of the image to 100% scale.
Step 3: Go to your Facebook account. Add image(s) and upload as usual. Images should look similar or exact when you saw it on Photoshop. Adding image(s) as an Album allows you to select or tick the High Quality option.