Are the switch pins going to make contact with anything on the other half of the controller when reassembled?
Are all of the wires free from places of movement or screw holes?
Are the solder joints correct and not dry?
Are all of the annoying black pieces of the controller back on their positioning pins?
Has your soldering iron made suitably sized black marks on your window ledge?
Four out of five is good enough to continue.
For a quick test, replace the battery and depress your switch all the way. If the player one led lights up very dimly, then the mod worked!
Now try putting it back together without breaking anything.