When I paste an image into photoshop it is blurry

I open a high quality photo in Photoshop. I then cut the section I want into another image (I am making a cover photo for Facebook 848 x 315 px). When I paste the image and scale it appropriately it appears to be pixalated when I zoom in. I am wondering is it when I set up a new image to paste it to, am I setting it up wrong?