Hope this helps anyone getting errors. Found it on a PS site.
“Selected your game from the Welcome Back package and didn’t get to pick your game? No problem! If this happened, go to the XMB and under the PlayStation Network column, go to Account Management>Transaction Management>Services List>SCEA Promotions to download the game for that first slot.”
On another note, the free PS+ service should be available for download within the store itself.
Also, the PS Store is probably being extremely overloaded due to the sheer amount of people downloading stuff. If you wait until later tonight, it'll probably calm down and you should see less errors.