Adding black to the bottom/sides of this photo

[ShannonV]

I know there is a simple solution to this. I want to extend the black background below baby, and possibly on the sides, so she is smaller in the frame. I was thinking I would have to place it on a new document and stretch the sides maybe? Not sure if this is the correct method though.

 

Photo has only raw edits done

[Damien Symonds]

No, just go to Image>Resize>Canvas Size.  Make it as big as you want - in fact, make it bigger than you want.

At the bottom, make sure the "Canvas Extension Color" is white.  I know it's tempting to make it black, but it's risky.  Leave it white.

Once you've done that, and hit OK, add a black Solid Color layer, then invert the mask, then paint the black onto those outside areas.  Use a nice biggish soft brush, so the new black blends with the existing black.

Lastly, turn that layer on and off a few times, to make darn sure none of your new black has encroached onto the baby.

[ShannonV]

Thanks! I knew you'd have a trick!