So confused about image size

You should think about images as having two or three sizes.   Images have an aspect ration size that is the relative length of the image sides  to each other the width and height relationship then there is image detail size.  To have  details you need Pixels to Store the details. You image canvas size pixels store your image details.  Pixel data is the Bulk of your Images file size.  thankfully there is a lot redundant details in most images like skys and walls so data compression can be used to reduce the Image files size. You trade some CPU time do some disk space.  With Disk buffering and cashing and write behind Processing can be much faster without using data compression.   Then there is  Image Print size the Pixel Print Density the the image's pixels are printed. By changing the Image Print PPI resolution you change the size pixels are printed. So you cams print a 3000px by 2000px image many print sizes.  All the prints will have a 3:2 landscape aspect ratio.  Here you see the Print size a 3000px by 2000px image will print using 300ppi print resolution 200ppi resolution and 100ppi resolution.

10" by 6.667"

15" by 10"

30" be 20"

All prints will likely have an acceptable print quality for the viewing distance they will be view from from.  The human eye can only  resolve down to 300PPI from a very close distance,   For large Prints you do not have to print at a 300ppi print resolution.   For fine details like hair, skin texture etc you need pixels that have those details stored.

Make sure you have not set any scaling in the print dialogue.

Dave

Could you please post a screenshot with the Image Size dialog visible? 

What were your print settings? (again screenshots might be helpful)