Add boarder/canvas size

So I'm new to photoshop and I am currently working to get my Cert. One of the lessons is to add a boarder to the photo and I know how to do that (Canvas Size) but everytime I try to do that, the photo resizes to the orginal photo size and shows some schuffs I had orginally cropped out... I included two images, 1st photo is what it should look it and 2nd phot is what mine looks like when I do it. Someone please help me out, thank you!