Mats can be added easily. If you are using a scrapkit, then you can cut out another bg paper to just bigger then your pic and use it as a mat.
I use PSP, not PS, but I also add borders and then decorate them. If you have that function, you can add a slim black border, like 1 or 2 pixels, depending on your picture size. Then add another border in a color not in your pic, I usually use white or red depending on the pic, much thicker 40 or more depending again on pic size, and then another add border with another slim black. I think highlight the middle border (white or red) and fill it with a pattern or a paper or even just a matching color. With sections highlighted you can add bevels and other things to create different looks.