That looks really good! Did you use the same method as Argos laid out? Can I ask how you replaced the sky rather than cloning it?
Yes I used a similar process with a few differences.
I first open the image document and made a selection of the subject (you) and removed the background.
I then opened another copy of the image in a new document.
I Used the Rectangle Tool to create a 1080 x 1350 rectangle.
I then made yet another selection of the subject and used a "Hide Selection" layer mask.
I then applied the layer mask, by right clicking the layer and selecting "apply layer mask".
I then removed the sky from the original image.
I placed the newly cropped background layer above the 1080 x 1350 rectangle and added a clipping mask.
On a new layer, I used the Gradient Tool to create the new sky.
Open the Gradient Editor, Use the foreground to background preset..
Change the color stops on the Gradient Editor or set the foreground and background by sampling the sky from original image.
Set the Gradient to linear.
Drag the gradient up or down while holding the shift key.
Watch this
VIDEO.
I then placed the new sky layer between the 1080 x 1350 rectangle layer and the Cropped background layer and added a clipping mask.
Next I switched back over to subject document and used the Move Tool to drag and drop the subject into the second document (on the tab).
I then used free transform to adjust and position the subject.
I saved this PSD file so I can go back to it for edits if needed.
All that remains to do is to crop the image with the snap function and "save as"........jpg, png, etc,.