What is the resolution of this composite ?
Looking at your posting, the top picture looks fairly sharp, the bottom picture with the dog does look blurry.
The rule of thumb is that for printing, it is desirable to have the resolution in the 240-300 px/in range. For posting on the web 72 px/in (minimum) should be ok.
If you decide to start over, increase the resolution of the components via Image>resize>image size with resampling & constrain proportions checked in the dialog. Also, the background layer (File>new>blank layer) should have the same resolution value.
If one of the pictures look blurry prior to any manipulation on your part, sharpen it prior to insertion.