How do I get exact border around photo?

[AnotherEarthling]

It's because the image height/width ratio is different compared to your actual medium.

Yes you're right. How do I resolve that issue?
I did get it to center and have a border around it. However, one again, the white on the border is more on the top and bottom of the photo then it is on the left and right side.

[Hoogle]

because your printig media is 6x 4 for example so you need to set up your photoshop document to be proportionate to that so if your media is 6 x 4 inches you need to mnake your photoshop document 6x 4 inches